Method and system for control of a patient&#39;s body temperature by way of transluminally insertable heat exchange catheter

ABSTRACT

Methods and apparatuses for temperature modification of a patient, or selected regions thereof, including inducing hypothermia. The temperature modification is accomplished using an in-dwelling heat exchange catheter within which a fluid heat exchange medium circulates. A heat exchange cassette of any one of several disclosed variations is attached to the circulatory flow lines of the catheter, the heat exchange cassette being sized to engage a cavity within one of various described re-usable control units. A temperature control scheme for ramping the body temperature up or down without overshoot is provided. The disposable heat exchange cassettes may include an integral pump head that engages with a pump drive mechanism within the re-usable control unit. More than one control unit may be provided to receive the same heat exchange cassette allowing substitution of a smaller, battery-powered unit for a large capacity control once the patient reaches the desired target temperature.

RELATED APPLICATIONS

This application is a Continuation-In-Part of U.S. patent applicationSer. No. 09/138,830, filed on Aug. 24, 1998 and also claims benefit ofpriority to U.S. application Ser. No., 09/563,946, filed on May 2, 2000,U.S. Provisional Application Ser. No. 60/185,561, filed Feb. 28, 2000,and U.S. application Ser. No. 60/219,922, filed Jul. 21, 2000, theentireties of which are expressly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to medical devices and methodsand, more particularly, to a programmable, microprocessor basedcontroller and method for controlling the temperature and flow of athermal exchange fluid that is circulated through a heat exchangecatheter inserted into a patient's body for the purpose or cooling orwarming at least a portion of the patient's body.

BACKGROUND OF THE INVENTION

Under ordinary circumstances, the thermoregulatory mechanisms of ahealthy human body serve to maintain the body at a constant temperatureof about 37° C. (98.6° F.), a condition sometimes referred to asnormothermia. To maintain normothermia, the thermoregulatory mechanismsact so that heat lost from the person's body is replaced by the sameamount of heat generated by metabolic activity within the body. Forvarious reasons such as extreme environmental exposure to a coldenvironment or loss of thermoregulatory ability as a result of diseaseor anesthesia, a person may develop a body temperature that is belownormal, a condition known as hypothermia. A person may develop acondition that is above normothermia, a condition known as hyperthermia,as a result of extreme exposure to a hot environment, or malfunctioningthermoregulatory mechanisms, the latter being a condition sometimescalled malignant hyperthermia. The body may also establish a set pointtemperature (that is, the temperature which the body's thermoregulatorymechanisms function to maintain) that is above normothermia, a conditionusually referred to as fever.

Accidental hypothermia is generally a dangerous condition that may evenbe life threatening, and requires treatment. If severe, for examplewhere the body temperature drops below 30° C., hypothermia may haveserious consequences such as cardiac arrhythmias, inability of the bloodto clot normally, or interference with normal metabolism. If the periodof hypothermia is extensive, the patient may even experience impairedimmune response and increased incidence of infection.

Simple methods for treating accidental hypothermia have been known sincevery early times. Such methods include wrapping the patient in blankets,administering warm fluids by mouth, and immersing the patient in a warmwater bath. If the hypothermia is not too severe, these methods may beeffective. However, wrapping a patient in a blanket depends on theability of the patient's own body to generate heat to re-warm the body.Administering warm fluids by mouth relies on the patient's ability toswallow, and is limited in the temperature of the liquid consumed andthe amount of fluid that may be administered in a limited period oftime. Immersing a patient in warm water is often impractical,particularly if the patient is simultaneously undergoing surgery or someother medical procedure.

More recently, hypothermia may be treated in a more complex fashion.Heated warming blankets may be applied to a patient or warming lampsthat apply heat to the skin of the patient may be used. Heat applied tothe patient's skin, however, has to transmit through the skin byconduction or radiation which may be slow and inefficient, and the bloodflow to the skin may be shut down by the body's thermoregulatoryresponse, and thus, even if the skin is warmed, such mechanisms may beineffective in providing heat to the core of the patient's body. Whenbreathing gases are administered to a patient, for example a patientunder anesthesia, the breathing gases may be warmed. This provides heatrelatively fast to the patient, but the amount of heat that can beadministered without injuring the patient's lungs is very limited. Analternative method of warming a hypothermic patient involves infusing ahot liquid into the patient via an IV infusion, but this is limited bythe amount of liquid that can be infused and the temperature of theliquid.

In extreme situations, a very invasive method may be employed to controlhypothermia. Shunts may be placed into the patient to direct blood fromthe patient through an external machine such as a cardiopulmonaryby-pass (CPB) machine which includes a heater. In this way, the bloodmay be removed from the patient, heated externally, and pumped back intothe patient. Such extreme measures have obvious advantages as toeffectiveness, but also obvious drawbacks as to invasiveness. Thepumping of blood through an external circuit that treats the blood isgenerally quite damaging to the blood, and the procedure is onlypossible in a hospital setting with highly trained personnel operatingthe equipment.

Accidental hyperthermia may also result from various conditions. Wherethe normal thermoregulatory ability of the body is lost, because ofdisease or anesthesia, run-away hyperthermia, also known as malignanthyperthermia, may result. The body may also set a higher than normal setpoint resulting in fever which is a type of hyperthermia. Likehypothermia, accidental hyperthermia is a serious condition that maysometimes be fatal. In particular, hyperthermia has been found to beneurodestructive, both in itself or in conjunction with other healthproblems such as traumatic brain injury or stroke, where a bodytemperature in excess of normal has been shown to result in dramaticallyworse outcomes, even death.

As with hypothermia, when the condition is not too severe, simplemethods for treating the condition exist, such as cold water baths andcooling blankets, or antipyretic drugs such as aspirin or acetaminophen,and for the more extreme cases, more effective but complex and invasivemeans such as cooled breathing gases, cold infusions, and blood cooledduring CPB also exist. These, however, are subject to the limitationsand complications as described above in connection with hypothermia.

Although both hypothermia and hyperthermia may be harmful and requiretreatment in some cases, in other cases hyperthermia, and especiallyhypothermia, may be therapeutic or otherwise advantageous, and thereforemay be intentionally induced. For example, periods of cardiac arrest orcardiac insufficiency in heart surgery result in insufficient blood tothe brain and spinal cord, and thus can produce brain damage or othernerve damage. Hypothermia is recognized in the medical community as anaccepted neuroprotectant and therefore a patient is often kept in astate of induced hypothermia. Hypothermia also has similar advantageousprotective ability for treating or minimizing the adverse effects ofcertain neurological diseases or disorders such as head trauma, spinaltrauma and hemorrhagic or ischemic stroke. Therefore it is sometimesdesirable to induce whole-body or regional hypothermia for the purposeof facilitating or minimizing adverse effects of certain surgical orinterventional procedures such as open heart surgery, aneurysm repairsurgeries, endovascular aneurysm repair procedures, spinal surgeries, orother surgeries where blood flow to the brain, spinal cord or vitalorgans may be interrupted or compromised. Hypothermia has even beenfound to be advantageous to protect cardiac muscle tissue after amyocardial infarct (MI).

Current methods of attempting to induce hypothermia generally involveconstant surface cooling, by cooling blanket or by alcohol or ice waterrubs. However, such cooling methods are extremely cumbersome, andgenerally ineffective to cool the body's core. The body's response tocold alcohol or ice water applied to the surface is to shut down thecirculation of blood through the capillary beds, and to the surface ofthe body generally, and thus to prevent the cold surface from coolingthe core. If the surface cooling works at all, it does so very slowly.There is also an inability to precisely control the temperature of thepatient by this method.

If the patient is in a surgical setting, the patient may be anesthetizedand cooled by CPB as described above. Generally, however, this is onlyavailable in the most extreme situations involving a full surgical teamand full surgical suite, and importantly, is only available for a shortperiod of time because of the damage to the blood caused by pumping.Generally surgeons do not wish to pump the blood for periods longer than4 hours, and in the case of stroke or traumatic brain damage, it may bedesirable to induce hypothermia for longer than a full day. Because ofthe direct control of the temperature of a large amount of blood, thismethod allows fairly precise control of the patient's temperature.However, it is this very external manipulation of large amounts of thepatient's blood that makes long term use of this procedure veryundesirable.

Means for effectively adding heat to the core of the body that do notinvolve pumping the blood with an external, mechanical pump have beensuggested. For example, a method of treating hypothermia or hyperthermiaby means of a heat exchange catheter placed in the bloodstream of apatient was described in U.S. Pat. No. 5,486,208 to Ginsburg, thecomplete disclosure of which is incorporated herein by reference. Meansof controlling the temperature of a patient by controlling such a systemis disclosed in U.S. Pat. No. 5,837,003, also to Ginsburg, the completedisclosure of which is incorporated herein by reference. A furthersystem for such controlled intervascular temperature control isdisclosed in publication WO 00/10494 to Ginsburg et al., the completedisclosure of which is incorporated herein by reference. Those patentsand publication disclose a method of treating or inducing hypothermia byinserting a heat exchange catheter having a heat exchange area into thebloodstream of a patient, and circulating heat exchange fluid throughthe balloon while the balloon is in contact with the blood to add orremove heat from the bloodstream. (As used herein, a balloon is astructure that may be readily inflated by increasing pressure in theballoon and collapsed by reducing pressure in the balloon vacuum.)

For the foregoing reasons, there is a need for a rapid and effectivemeans to add or remove heat from the fluid supply for a catheter used tocontrol the body temperature of a patient in an effective and efficientmanner, while avoiding the inadequacies of the prior art methods. Inparticular, a fluid source that rapidly, efficiently and controllablyregulates a disposable source of fluid based on feedback from thetemperature of the patient or target tissue within the patient would bea great advantage.

SUMMARY OF THE INVENTION

The invention provides for modification and control of the temperatureof a patient, or selected portions of a patient, including controllablyinducing a state of hypothermia in the patient. The invention alsoprovides for controllably warming a patient in whom a state of reducedtemperature, or hypothermia, has been induced.

In one embodiment, the present invention includes a heat transfercatheter insertable into a patient, a disposable heat exchange plate,conduits coupled to the heat transfer catheter and heat exchange platethat enable circulation of a heat exchange medium therebetween, and amaster control unit housing a heater/cooler unit within and having aslot, the slot being sized so that the disposable heat exchange platecan be installed therethrough into the master control unit and intothermal communication with the heater/cooler unit, wherein theheater/cooler unit can influence the temperature of the patient via thedisposable heat exchange plate, conduits, and heat transfer catheter.

In another embodiment, the invention includes a heat transfer catheterinsertable into a patient, a disposable heat exchange unit having afluid pathway therewithin and incorporating an integral pump headadapted to move fluid through the fluid pathway, conduits coupled to theheat transfer catheter and heat exchange unit that enable circulation ofa heat exchange medium therebetween upon operation of the pump head, anda reusable master control unit having a heater/cooler and a pump driver,the disposable heat exchange unit being adapted to couple to the mastercontrol unit such that the pump driver engages the integral pump headand so that the fluid pathway is in thermal communication with theheater/cooler.

In another embodiment, the present invention may also include aplurality of sensors that supply patient data, such as the patient'stemperature, to a master control unit that is adapted, configured orprogrammed to operate a heater/cooler based on the supplied patientdata. The master controller may include a microprocessor that isresponsive to the sensors to provide control signals to theheater/cooler. The microprocessor may also be configured or programmedto compare signals from at least two of the sensors and produce an alarmsignal if the signals do not agree.

In still another embodiment, the microprocessor may receive a targettemperature input and a sensor signal that represents a sensed patienttemperature. The microprocessor is configured or programmed to add heatto the heat exchange medium if the target temperature is above thepatient temperature and remove heat from the heat exchange medium if thetarget temperature is below the patient temperature in response to thesignal from the sensor with a proportional integrated differential (PID)response such that the rate at which patient temperature approaches thetarget temperature is controlled.

In another embodiment the present invention provides a method forregulating the temperature of at least a portion of a patient. Themethod includes providing a disposable heat transfer catheter and heatexchange unit coupled via conduits that enable circulation of a heatexchange medium therebetween, providing a master control unit housing aheater/cool unit within and having a slot, installing the heat exchangeunit through the slot into the master control unit and into thermalcommunication with the heater/cooler unit, inserting the heat transfercatheter into the patient, circulating fluid between the heat transfercatheter and heat exchange unit in the master control unit, andtransferring heat between the heat exchange unit and a heater/coolerunit so as to regulate the temperature of the patient via the heattransfer catheter.

In still another embodiment, the method of regulating the temperature ofat least a portion of a patient may include sensing the patient's bodytemperature, providing a heat transfer region on the heat transfercatheter, the heat exchange plate, heater/cooler, and pump head beingadapted to flow heat exchange medium through the conduits to elevate ordepress the temperature of the catheter heat transfer region relative tothe body temperature, selecting a target temperature different than thebody temperature, selecting a ramp rate equal to the time rate of changeof temperature from the body temperature to the target temperature,setting the temperature of the heat exchange medium within the catheterheat transfer region based on the ramp rate, monitoring the temperaturedifferential between the target temperature and the body temperature,and reducing the ramp rate when the temperature differential reducesbelow a predetermined threshold.

In yet another embodiment, the present invention provides a method ofcirculating a heat exchange medium through a heat transfer catheterinstalled in the body of a patient, the method including providing adisposable heat transfer catheter and heat exchange unit coupled viaconduits that enable circulation of a heat exchange medium therebetween,the heat exchange unit incorporating an integral pump head adapted tocirculate fluid through the conduits, providing a reusable mastercontrol unit having a pump driver, coupling the heat exchange unit tothe master control unit such that the pump driver engages the integralpump head, inserting the heat transfer catheter into the patient, andactuating the pump driver to circulate fluid between the heat transfercatheter and heat exchange unit.

Other features and advantages of the present invention will become moreapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, which illustrate, by way of example, theprinciples of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a patient undergoing treatment using asystem in accordance with the present invention;

FIG. 2 is a schematic illustration of a disposable heat exchangecassette attached to a heat exchange catheter and an external fluidsource, and positioned for insertion into a suitable opening in are-usable master control unit of the present invention;

FIGS. 3A-3B together show a flowchart of a control scheme of the heatexchange system of the present invention;

FIG. 4 is a graph of the sensed temperature of a target tissue or bodyfluid over time under the influence of the control scheme of FIGS.3A-3B;

FIG. 5A is a perspective view of an exemplary re-usable control unit ofthe present invention;

FIG. 5B is a perspective view of an upper portion of the control unit ofFIG. 5A;

FIG. 5C is a plan view of an exemplary control panel for the controlunit of FIG. 5A;

FIGS. 5D-5F are perspective views of a lower portion of the control unitof FIG. 5A having exterior panels removed to expose interior components;

FIG. 5G is a perspective view of the control unit lower portion andshowing a heat exchange cassette-receiving subassembly exploded above aninner cavity;

FIGS. 6A-6C are various perspective and exploded views of the heatexchange cassette-receiving subassembly seen in FIG. 5G;

FIGS. 7A-7D are various perspective views of a lower guide assembly andpump drive mechanism of the heat exchange cassette-receiving subassemblyof FIG. 6A;

FIG. 8 is a schematic diagram of an exemplary control circuit of thepresent invention;

FIG. 9 is a perspective view of a disposable heat exchange cassetteattached to a heat exchange catheter and an external fluid source, andpositioned for insertion into a suitable opening in the reusable mastercontrol unit of the present invention;

FIG. 10A is an exploded view of a first disposable heat exchangecassette for use in the present invention;

FIG. 10B is a plan view of one end of the heat exchange cassette of FIG.10A illustrating fluid flow through a bulkhead and attached externalheat exchanger;

FIG. 10C is an exploded perspective view of a reservoir section of thebulkhead of FIG. 10B;

FIG. 10D is a schematic plan view of a fluid pressure damper of thebulkhead of FIG. 10B;

FIGS. 11A and 11B are sectional views take along line 11—11 through theexternal heat exchanger of FIG. 10A, and showing the heat exchanger inits uninflated and inflated states, respectively;

FIGS. 12A-12B are inverted perspective views of an exemplary fluidfitting for use with the external heat exchanger of FIG. 10A;

FIG. 13A is an exploded view of a second disposable heat exchangecassette for use in the present invention;

FIG. 13B is a plan view of one end of the heat exchange cassette of FIG.13A illustrating fluid flow through a bulkhead assembly and attachedexternal heat exchanger;

FIGS. 13C-13D are plan and sectional views, respectively, of thebulkhead assembly of FIG. 13B;

FIG. 13E is an exploded perspective view of a reservoir section of thebulkhead assembly of FIG. 13B;

FIG. 14A is a perspective exploded view of a feedblock section of thebulkhead assembly of FIG. 13B;

FIGS. 14B-14C are plan and sectional views, respectively, of thefeedblock section of FIG. 14A illustrating in hidden lines a fluidpressure regulating mechanism therein;

FIGS. 14D and 14E are vertical sectional views through a priming valvemechanism of the feedblock section of FIG. 14A;

FIGS. 14F and 14G are sectional views taken alone lines 14F and 14Grespectively of the view of FIG. 14C;

FIG. 15A is a perspective exploded view of a pump section of thebulkhead assembly of FIG. 13B;

FIG. 15B is a plan view of the pump section of FIG. 15A;

FIG. 15C is a sectional view through the pump section taken along line15C—15C of FIG. 15B;

FIG. 15D is a schematic plan view of the geometry of a pump head withinthe pump section of FIG. 15A;

FIGS. 16A-16C are elevational views of alternative embodiments of a pumpvane for use in the pump section of FIG. 15A;

FIGS. 17A-17B are plan and elevational views, respectively, of a pumphead driven gear engaged with a drive mechanism of the re-usable controlunit; and

FIGS. 18A-18C are schematic illustrations of the fluid flow usingdifferent embodiments of the disposable heat exchange cassette ofpresent invention.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention includes a catheter placed in the bloodstream of apatient for regulating the patient's body temperature, although those ofskill in the art will understand that various other applications for thesystem of the present invention are possible. In a preferredapplication, one or more of the heat exchange catheters of the presentinvention are positioned within a patient's vasculature to exchange heatwith the blood in order to regulate the overall body temperature, or toregulate the temperature of a localized region of the patient's body.Heat exchange fluid is then circulated through the catheter to exchangeheat between the blood and the heat exchange fluid, and a controllermanages the functioning of the system. The catheters may be, forexample, suitable for exchanging heat with arterial blood flowing towardthe brain to cool the brain, and may thus prevent damage to brain tissuethat might otherwise result from a stroke or other injury, or coolingvenous blood flowing toward the heart to cool the myocardium to preventtissue injury that might otherwise occur following an MI or othersimilar event.

In general, the invention provides a control unit and method forcontrolling the temperature and flow of heat transfer fluid for a heattransfer catheter used for controlling the body temperature of apatient. The control unit initially supplies heat transfer fluid to theheat transfer catheter to prime the heat exchange catheter for use. Italso receives input from the user, receives temperature information fromsensors that sense patient temperature information, and based thereon,controls the temperature of the heat transfer fluid. Further, based onfeedback from a pump in a cassette containing the heat transfer fluid,the control unit supplies heat transfer fluid at a relatively constantpressure. The cassette and the controller, working together, haveseveral warning or alarm states that warn the user of dangeroussituations, for example, by shutting down the pump motor and notifyingthe user if the fluid level in the cassette is unacceptably low.

Overview of Heat Exchange System

Any suitable heat exchange catheter may be utilized in a heat exchangesystem for regulating the temperature of a patient or a region of thepatient's body and controlled by the control unit as disclosed herein.In addition to the catheters disclosed herein, and by way ofillustration and not of limitation, catheters that may be utilized inthis invention are the catheters disclosed in U.S. Pat. No. 5,486,208 toGinsburg, U.S. Pat. No. 5,837,003 to Ginsburg, WO 00/10494 to Ginsburget al., and U.S. Pat. No. 5,624,392 to Saab, the complete disclosure ofeach of which is hereby incorporated in full herein by reference. Oneexample of such a heat exchange catheter system 20 is shown in FIG. 1,and includes a catheter control unit 22 and a heat exchange catheter 24formed with at least one heat transfer section 44. The heat transfersection or sections are located on that portion of the catheter 24, asillustrated by section 26, that is inserted into the patient. Thisinsertion portion is less than the full-length of the catheter andextends from the location on the catheter just inside the patient, whenthe catheter is fully inserted, to a distal end of the catheter. Thecatheter control unit 22 may include a fluid pump 28 for circulating aheat exchange fluid or medium within the catheter 24, and a heatexchanger component for heating and/or cooling circulating fluids withinthe heat transfer system 20. A reservoir or fluid bag 30 may beconnected to the control unit 22 to provide a source of heat transferfluid such as, saline, blood substitute solution, or other biocompatiblefluid. A circulatory heat exchange flow channel within the catheter maybe respectively connected to inlet 32 and outlet 34 conduits of the pump28 for circulation of the heat transfer fluid through the balloon tocool the flow of fluid within a selected body region. A similararrangement may be implemented for heating of selected body regionssimultaneously or independently of each other using the coolingcomponent of the system. The control unit 22 may further receive datafrom a variety of sensors which may be, for example, solid-statethermocouples, thermistors or other temperature sensitive sensingdevices to provide feedback from the catheter and various sensors toprovide patient temperature information representing core temperature ortemperature of selected organs or portions of the body. For instance,sensors may include a temperature probe 36 for the brain or head region,a rectal temperature probe 38, an ear temperature probe 40, anesophageal temperature probe (not shown), a bladder temperature probe(not shown), and the like.

Based upon sensed temperatures and conditions, the control unit 22 maydirect the heating or cooling of the catheter in response. The controlunit 22 may activate a heat exchanger at a first sensed temperature toheat fluid which is then circulated through the balloon, and may alsode-activate the heat exchanger at a second sensed temperature which maybe relatively higher or lower than the first sensed temperature or anyother predetermined temperature. Alternatively, the control unit mayactively cool the heat exchange fluid to cool the balloon. The controlunit 22 may operate multiple heat transfer units to independently heator cool different selected heat transfer sections of the heat exchangecontroller to attain desired or preselected temperatures in bodyregions. Likewise, the controller 22 may activate more than one heatexchanger to control temperature at particular regions of the patient'sbody. The controller might also activate or de-activate other apparatus,for example external heating blankets or the like, in response to sensedtemperatures.

The regulation exercised over the heat transfer catheters or otherdevices may be a simple on-off control, or may be a significantly moresophisticated control scheme including regulating the degree of heatingor cooling, resulting ramp rates of heating or cooling, or proportionalcontrol as the temperature of the heat exchange region or patientapproaches a target temperature, or the like.

The catheter control unit 22 may further include a thermoelectric coolerand heater (and associated flow conduits) that are selectively activatedto perform both heating and cooling functions with the same or differentheat transfer mediums within the closed-loop catheter system. Forexample, a first heat transfer section 42 located on the insertionportion 26 of at least one temperature regulating catheter 24 maycirculate a cold solution in the immediate head region, oralternatively, within a carotid artery or other blood vessel leading tothe brain. The head temperature may be locally monitored withtemperature sensors 36 positioned at a relatively proximate exteriorsurface of the patient or within selected body regions. Another heattransfer section 44 of the catheter 24, also located on the insertionportion 26, may circulate a heated solution within a collapsible balloonor otherwise provide heat to other body locations through heat elementsor other mechanisms described in accordance with other aspects of theinvention. While heat exchange catheter 24 may provide regionalhypothermia to the brain region for neuroprotective benefits, otherparts of the body may be kept relatively warm so that adverse sideeffects such as discomfort, shivering, blood coagulopathies, immunedeficiencies, and the like, may be avoided or minimized. Warming of thebody generally below the neck may be further achieved by insulating orwrapping the lower body in a heating pad or blanket 46 while the headregion above the neck is cool. It should be understood that multipleheat exchange sections of the catheter 24 may be modified to providewhole body cooling or warming to affect body core temperature.

Exemplary Heat Exchange System

The present invention contemplates the use of a re-usable controller orcontrol console having a heater/cooler device therein and which receivesa disposable heat exchange element coupled via conduits to a distalin-dwelling heat exchange catheter. More specifically, in one embodimentthe controller desirably includes an outer housing having an opening orslot for receiving the heat exchange element therewithin, the openingand housing ensuring reliable positioning of the heat exchange elementin proximity with the heater/cooler device. In this manner, set up ofthe system is facilitated because the operator only needs to fullyinsert and seat the heat exchange element into the controller opening inorder to couple the re-usable and disposable portions of the system.While the system is shown having a slot to receive the cassette, otherarrangements are possible so long as the cassette is kept it in closeproximity to the heat exchange element.

In an exemplary embodiment, FIG. 2 illustrates a heat exchange cathetersystem that includes a re-usable catheter control unit 50 and aplurality of disposable components including a heat exchange catheter52, a heat exchange element 54, a saline bag 56, sensors 58 a, 58 b andassociated wires 60 a, 60 b, and a plurality of fluid flow conduitsincluding a two-way conduit 62 extending distally from the heat exchangeelement 54. The re-usable catheter control unit 50 includes an outerhousing 64 within which is provided a heater/cooler 66, a pump driver68, and a controller processor 70. In addition, a manual input unit 72enables an operator to enter desirable operating parameters of thecontroller, for example a pre-selected temperature for the brain. Eachof the electronic devices provided within the control unit 50communicate through suitable wiring.

The heat exchange catheter 52 is formed with a catheter flow line 74 anda heat exchanger 76 which may be, for example, a heat exchange balloonoperated using a closed-loop flow of a biocompatible fluid that servesas the heat exchange medium. The catheter 52 may include a working lumen(not shown) for injection of drugs, fluoroscopic dye, or the like, andfor receipt of a guidewire 78 for use in placing the catheter at anappropriate location in the patient's body. A sensor 80 may be providedon the catheter 52 distal to the heat exchanger 76 to monitor thetemperature of the heat exchange balloon, and other sensors (not shown)may be provided as desired to monitor the blood temperature at thedistal tip of the catheter, at the proximal tip of the balloon, or atany other desired location along the catheter. The proximal end of thecatheter flow line 74 may be connected to a multi-arm adapter 82 forproviding separate access to various channels in the catheter 52. Forexample, a first arm 84 may provide access to the working lumen of thecatheter 52 for insertion of the guidewire 78 to steer the heat exchangecatheter to the desired location. Where the heat exchanger 76 is a heatexchange balloon for closed-loop flow of a heat exchange medium, theadapter 82 may contain a second arm 86 connected to an inflow line 88,and a third arm 90 connected to an outflow line 92. The inflow line 88and outflow line 92 are therefore placed in flow communication withrespective inflow and outflow channels (not shown) provided in the flowline 74 and heat exchanger 76. In this regard, the inflow and outflowlines 88, 92 may come together to form the single dual channel flow line62 connected to the heat exchange element 54. Furthermore, an externalfluid source such as the saline bag 56 may be placed in fluidcommunication with the outflow line 92 via a conduit 94 a and aT-junction 94 b. As will be explained further below, the external fluidsource is used to prime the closed-loop heat exchange balloon system.Alternatively, the external fluid source may be directly connected tothe heat exchange unit 54.

Still with reference to FIG. 2, the heat exchange unit 54 desirablyincludes a heat exchange plate 96 and a pump head 98. The pump head 98pumps heat exchange fluid through a serpentine fluid pathway 100 in theheat exchange plate 96, and through the associated flow lines andcatheter 52. As mentioned, the heat exchange unit 54 is configured toinstall into the re-usable catheter control unit 50. In this regard, theheat exchange unit 54 is desirably plate-shaped and sized to fit throughan elongate slot 102 in the control unit housing 64. Once inserted, thepump head 98 is placed in proximity to and engaged with the pump driver68, and the heat exchange plate 96 is placed in proximity to and inthermal communication with the heater/cooler 66. A solid-statethermoelectric heater/cooler 66 is particularly advantageous because thesame unit is capable of either generating heat or removing heat bysimply changing the polarity of the current activating the unit.Therefore, the heater/cooler 66 may be conveniently controlled so as tosupply or remove heat from the system without the need for two separateunits.

The pump driver 68 engages and activates the pump head 98 to cause it tocirculate heat exchange fluid through the heat exchange unit 54 and theserpentine path 100 in the heat exchange plate 96. Therefore, when theheat exchanger unit 54 is properly installed in the control unit 50, theheater/cooler 66 may act to heat or cool the heat exchange fluid as thatfluid is circulated through the serpentine pathway 100 and thereafterthrough the flow lines leading to the in-dwelling heat exchanger 76.When the heat exchange fluid is circulated through the heat exchanger 76located in the patient's body, it may act to add or remove heat from thebody. In this way, the heater/cooler 66 regulates the blood temperatureof the patient as desired.

The heater/cooler 66 and a pump driver 68 are responsive to thecontroller processor 70. The processor 70 receives data input throughelectrical connections 104 to numerous sensors, for example bodytemperature sensors 58 a, 58 b positioned to sense the temperature atvarious locations within the patient. For example, the temperature maybe sensed at the patient's ear, brain region, bladder, rectum,esophagus, or other appropriate location as desired by the operator.Also, as mentioned, a sensor 80 may monitor the temperature of the heatexchanger 76, and other sensors along the catheter 52 may provide inputto the controller processor 70, such as via a wire 60 c. Additionally,by means of the manual input unit 72, an operator provides the operatingparameters of the control system such as, for example, a pre-selectedtemperature for the brain and/or the whole body of the patient. Theoperator input parameters are communicated to the controller processor70 by means of appropriate wiring. The controller processor 70coordinates the various data received and selectively actuates theseveral operational subsystems to achieve and maintain desired results;i.e., proper regulation of the patient's body temperature. For example,the processor 70 may actuate the heater/cooler 66 to increase the amountof heat it is removing if the actual temperature is above the specifiedtemperature, or it may decrease the amount of heat being removed if thetemperature is below the specified temperature. Alternatively, theprocessor 70 may stop the pumping of the heat exchange fluid when thesensed body or regional temperature reaches the desired temperature.Referring still to FIG. 2, the disposable heat exchange unit 54 of theinvention is shown as being attached to a heat exchange catheter 52 andexternal fluid source 56 is positioned in cooperation with a suitablereusable master control unit 50. Prior to commencing treatment, the heatexchange unit 54 is inserted into the reusable master control unit 50,the external fluid source 56 is attached to the fill port and the pump98 is automatically or passively primed and the disposable systemfilled, after which the catheter is ready for insertion in thevasculature of the patient, for example in the inferior vena cava or thecarotid artery. Chilled or warmed biocompatible fluid, such as saline,is pumped into the closed circuit catheter which exchanges heat directlywith the patient's blood. The control unit serves to automaticallycontrol the patient's temperature. Once treatment with the catheter iscomplete, the catheter is removed from the patient and the cassette isremoved from the reusable master control unit. Both the catheter andcassette are then discarded. The reusable master control unit, however,which never comes into direct contact with the heat exchange fluid, isready for immediate use for treatment on other patients, along with anew cassette and catheter and fresh external fluid source.

Exemplary Method of Temperature Control

The flowchart seen in FIGS. 3A and 3B illustrates an exemplary sequenceof steps that the controller processor 70 coordinates during temperatureregulation of a patient. First, in step 110, a target temperature forthe target tissue (which may be the entire body) is selected, generallyby user input. Steps 112 a and 112 b involve determination of an uppervariance set point and a lower variance set point, respectively. This isgenerally a pre-set buffer range above and below the target temperaturethat is built or programmed into the controller processor. Thesevariance set points straddle the target temperature and create a bufferrange of temperature within which the controller operates.

More specifically, the sensed temperature for the target tissue isobtained in step 114 prior to or after step 116 in which a heatexchanger capable of either heating or cooling body fluid is placed inproximity with body fluid that subsequently flows to the target tissue.Based on user input, or on a comparison between the target temperatureand the sensed tissue temperature, a determination is made in step 118as to whether the heat exchanger will be operating a cooling mode, aheat mode, or will remain off. That is, if the target temperature equalsthe tissue temperature then there will be no need to initially heat orcool the body fluid. The determination step 118 leads to three differentmodes of operation of the system, depending on whether the system willbe COOLING, HEATING, or OFF. These modes of operation correspond tosteps 120 a, 120 b, and 120 c, which appear on both the FIGS. 3A and 3B.

If the system is in the COOLING mode, the flowchart logic leads to step120 a which compares the sensed tissue temperature with the pre-selectedtarget temperature. If the tissue temperature is greater than the targettemperature, the system continues cooling as indicated in step 122, andthe processor 70 returns to decision step 118. On the other hand, if thesensed tissue temperature is equal to or less than the targettemperature, the heat exchanger is converted to the OFF mode asindicated in step 124 and the processor 70 returns to decision step 118.

If the system is in the HEATING mode, the flowchart logic leads to step120 b which also compares the sensed tissue temperature with thepre-selected target temperature. If the tissue temperature is less thanthe target temperature, the system continues heating as indicated instep 126, and the processor 70 returns to decision step 118. On theother hand, if the tissue temperature is equal to or greater than thetarget temperature, the heat exchanger is converted to the OFF mode asindicated in step 128, and the processor 70 returns to decision step118. If the system is in the OFF mode, the flowchart logic leads to step120 c which compares the sensed tissue temperature with the uppervariance temperature set point. Then, if the sensed tissue temperatureis equal to or greater than the upper variance set point, the system isconverted to the COOLING mode as indicated in step 130, and theprocessor 70 returns to decision step 118. If the tissue temperature isless than the upper variance set point, the processor continues to step132 in the flowchart logic, and determines if the tissue temperature isequal to or less than the lower variance set point, whereby the systemis converted to the HEATING mode and processor 70 returns to decisionstep 118. Finally, if the tissue temperature is between the upper andlower variance set points, the system does nothing as indicated in step134, and the processor 70 returns to decision step 118.

FIG. 4 is a graphical illustration plotting the fluctuating sensedtissue temperature over a period of time relative to the targettemperature and variance set points. In the example, the targettemperature is set at 31 degrees Celsius, with the upper and lowervariance set points ½ degrees on either side. Initially, the sensedtissue temperature is greater than the target temperature, such as ifthe heat exchange catheter is placed in contact with blood at 37 degreesCelsius. The system is first placed in the COOLING mode so that thesensed tissue temperature is reduced until it equals the targettemperature at 136, corresponding to steps 120 a and 124 in FIG. 3A. Instep 124, the heat exchanger is converted to the OFF mode, which resultsin the sensed tissue temperature climbing until it reaches the uppervariance set point at 138, corresponding to step 130 in FIG. 3B, atwhich time the system begins cooling again. This cycle is repeated inthe region indicated at A.

Eventually, the patient may be unable to maintain even the targettemperature as shown by the temperature profile in the region indicatedat B. For example, after the sensed tissue temperature reaches thetarget temperature at 140, and the heat exchanger is turned OFF, thesensed target temperature may continue to drift lower until it reachesthe lower variance set point at 142. The controller logic senses this instep 132 of FIG. 3B, and converts the system to the HEATING mode.Subsequently, the sensed tissue temperature climbs to the targettemperature at 144, and the system is again turned OFF, corresponding tosteps 120 b and 128 in FIG. 3B. Alternatively, depending on the patientand the situation, it may be that after the sensed tissue temperaturereaches the target temperature and the heat exchanger is turned OFF, thepatient's temperature may begin to increase until it rises to the uppervariance set point temperature, at which point, as described in box 130,the heat exchanger begins to COOL. As can be appreciated, the sensedtissue temperature continues to fluctuate between the upper and lowervariance set points in this manner.

The control scheme as applied to the system of the present invention hasthe advantage of allowing the operator to essentially input a desiredtemperature after which time the system will automatically regulate thetissue temperature until it reaches the target temperature, and willmaintain the tissue temperature at that target temperature. The bufferrange created by the upper and lower variance set points prevents thecontroller from turning the heater/cooler on and off or activating andde-activating the pump driver in rapid succession, actions that would bepotentially damaging to these electric devices.

It should also be understood, in accordance with the present invention,that the controller processor 70 may be configured to simultaneouslyrespond to multiple sensors, or to activate or de-activate variouscomponents such as several heat exchangers. In this way, for example, acontroller might heat blood that is subsequently circulated to the corebody in response to a sensed core body temperature that is below thetarget temperature, and simultaneously activate a second heat exchangerto cool blood that is directed to the brain region in response to asensed brain temperature that is above the target temperature. It may bethat the sensed body temperature is at the target temperature and thusthe heat exchanger that is in contact with blood circulating to the bodycore may be turned off by the controller, while at the same time thecontroller continues to activate the second heat exchanger to cool bloodthat is directed to the brain region. Any of the many control schemesthat may be anticipated by an operator and programmed into the controlunit are contemplated by this invention.

A further advantage of the system of the present invention is that allof the portions of the system that are in contact with the patient aredisposable, but substantial and relatively expensive portions of thesystem are reusable. Thus, the catheter, the flow path for sterile heatexchange fluid, the sterile heat exchange fluid itself, and the pumphead are all disposable. Even if a rupture in the heat exchange balloonpermits the heat exchange fluid channels and thus the pump head to comein contact with a patient's blood, no cross-contamination will occurbetween patients because all those elements are disposable. The pumpdriver, the electronic control mechanisms, the thermoelectric cooler,and the manual input unit, however, are all reusable for economy andconvenience. Desirably, as illustrated, all of these re-usablecomponents are housed within a single control unit 50. Likewise, thevarious sensors distributed around a patient's body and along thecatheter may be disposable, but the controller processor 70 to whichthey attach is re-usable without the need for sterilization.

It will also be appreciated by those of skill in the art that the systemdescribed herein may be employed using numerous substitutions,deletions, and alternatives without deviating from the spirit of theinvention as claimed below. For example, but not by way of limitation,the serpentine pathway 100 in the heat exchange plate 96 may be a coilor other suitable configuration, or the sensors may sense a wide varietyof body locations and other parameters may be provided to the processor70, such as temperature or pressure. Further, the in-dwelling heatexchanger 76 at the end of the catheter 52 may be any appropriate type,such as a thermoelectric heating/cooling unit which would not requirethe circulation of a heat exchange fluid. If a heat exchange balloon isprovided, a pump might be provided that is a screw pump, a gear pump, adiaphragm pump, a peristaltic roller pump, or any other suitable meansfor pumping the heat exchange fluid. All of these and othersubstitutions obvious to those of skill in the art are contemplated bythis invention.

Exemplary Heat Exchange Catheter Control Unit

FIGS. 5A-5F are various views of an exemplary heat exchange cathetercontrol unit 150 of the present invention that is particularly suitedfor rapid temperature regulation of a patient. As seen in the FIGS., thecontrol unit 150 comprises a vertically-oriented outer housing having alower portion 152 and upper portion 154 separated at a generallyhorizontal dividing line 156 located close to the top of the unit. Thelower portion 152 is mounted on wheels 158 for ease of portability, withthe wheels preferably being of the swivel type having foot-actuatedlocks. For ease of servicing, the upper and lower portions may be joinedtogether with hinges 155 at the back so that the top portion may belifted up and rotated back to expose the interior of the unit. In anexemplary embodiment, the control unit 150 has a height that enables anoperator to easily access an upper control panel 160 without significantbending over. For example, the control unit 150 may have a total heightof between approximately 2-3 feet, and preferably about 32 inches. Thesubstantially horizontal cross-section of a majority of the control unit150 may have widths of between one and two feet, although the lowerportion 152 preferably widens at its lower end with the wheels 158mounted on the lower corners to provide greater stability.

FIG. 5A illustrates the assembled control unit 150, while FIGS. 5B-5Gshow various exploded views and subassemblies of the control unit. FIG.5A illustrates the front and right sides of the unit 150 wherein thecontrol panel 160 is visible on an angled upper panel 162 of the upperportion 154 front side. The angled upper panel 162 also defines a fluidcontainer receiving cavity 164 adjacent the control panel 160. Further,a plurality of handles 166 may be provided to help maneuver the controlunit 150. of the control unit 150, just below the horizontal dividingline 156. As will be explained below, the opening 168 is sized andshaped to receive a heat exchange cassette of the present invention,analogous to the heat exchange cassette-receiving opening 102 shown inFIG. 2. Likewise, the control unit 150 provides all of the features thatwere described above for the control unit 50 of FIG. 2, including aheater/cooler, a pump driver, a controller processor, and a manual inputunit, namely the control panel 160.

Because of the relatively high capacity for heat and cooling, the lowerportion 152 of the control unit housing includes a plurality of vents170 to facilitate convective heat exchange between the interior of thehousing and the surrounding environment. The control unit housing maybemanufactured of a number of suitably strong and corrosion-resistantmaterials, including stainless-steel, aluminum, or molded plastic.Desirably, the components of the control unit 150 are adapted to run onconventional power from a catheterization lab power outlet, for example.

The present invention also contemplates the use of two different controlunits in series, depending on need. For example, the control unit 150 ofFIGS. 5A-5F having a relatively large heat transfer capacity and largehousing can be used initially to rapidly alter the patient's bodytemperature. Subsequently, a smaller unit having an internal batterypower source can be substituted for convenience and economy. Both thelarge and small control units desirably define the same sized andconfigured cavity for receiving a cassette of the present invention. Inthis manner, the cassette need only be de-coupled from one of the unitsand coupled to the other unit for the transfer.

Exemplary Control Panel

FIGS. 5B and 5C illustrate in greater detail the upper portion 154 ofthe control unit 150, and in particular the control panel 160. FIG. 5Bshows a facade 172 exploded from the control panel 160, with the facadeshown in FIG. 5C having labels printed thereon corresponding to variousdisplays and buttons. (The reader will notice that the control panel 160in FIG. 5C is an alternative embodiment from the one shown in the restof the drawings, and includes several added features and with severalbuttons and/or displays being slightly relocated). The following is adescription of the physical characteristics of the control panel 160,with a description of an exemplary method of using the control panel tofollow later in the description.

The exemplary control panel 160 of FIG. 5C provides a number of visualdisplays, including, from top to bottom along the centerline, a patienttemperature display 174, a target temperature display 176, acooling/warming rate display 178, and a system feedback/status display180. Other desirable information may be displayed, either with anadditional display, or alternating with information displayed on one ofthe screens shown here, or by user initiated request from one of thescreens shown here. For example, by way of illustration but notlimitation, if the ramp rate for heating or cooling the patient is setby the user, or is calculated by the control microprocessor, or theprojected time to target temperature is calculated, those values may beshown. The larger displays for alphanumeric characters are preferablyliquid crystal displays (LCD), while several light emitting diode (LED)status indicators are also provided. Several graphic icons arepositioned adjacent the left of the upper three LCD displays 174,176,and 178, to indicate their respective display functions. Specifically, apatient temperature icon 182 a, a target temperature LED 182 b, and acooling/warming rate LED 182 c are provided. Just below thecooling/warming rate LED 182 c, an operational mode LED 182 d andassociated vertical series of three mode indicators 184 are provided.Only one of the indicators 184 lights up at any one time, depending onwhether the system is in the COOLING, WARMING, or MAINTAINING mode. Inlieu of the mode indicators 184, the display 180 may carry the messageCOOLING PATIENT, WARMING PATIENT, or MAINTAINING so that the operatorcan easily identify the mode of functioning of the controller. Therealso may be only one patient temperature icon 182 which has a line oflights that streams upward if the unit is warming, downward if the unitis cooling, and blinks stationary if the unit is maintaining. Finally, apower on/off indicator LED is provided in the lower left corner of thecontrol panel 160.

The control panel 160 also exhibits a number of input buttons including,in descending order on the right side of the control panel, aCelsius/Fahrenheit display toggle 190, a pair of target temperatureadjustment buttons 192, a pair of cooling/warming rate adjustmentbuttons 194, a multi-function/enter button 196, and a mute audible alarmbutton 198. The mute audible alarm button 198 is nested within an LEDalarm indicator 200. Finally, in the lower central portion of thecontrol panel 160, a stop system operation button 202 permits instantshutdown of the system.

Control Unit Housing

As seen in FIGS. 5D-5G, the control unit housing is defined by a numberof panels, some of which can be removed to view and access the interiorcontents of the control unit 150. For example, in FIGS. 5D and 5F, thefront panel 169 (FIG. 5A) has been removed to expose an internal cavity210 a majority of which is filled by a subhousing 212 enclosing arelatively large blower fan (not shown). As will be explained below, theblower fan within the subhousing 212 interacts with a thermoelectriccooler/heater, and is separated therewith by a first filter (not shown)spanning a circular upper opening 214 and held thereon by a gasket 216.A second air filter 218 covers a square opening 220 in the bottom of thesubhousing 212 within the control unit such that air blown (upward ordownward) through the circular opening 214 is double filtered. Finally,a drain cup 222 may be provided in the bottom of the control unit 150.In FIG. 5E a rear panel has been removed to expose a rear cavity 224from which a number of electric connectors 226 are accessible.

FIG. 5G is a frontal perspective view of the lower portion 152 of thecontrol unit 150 showing a heat exchange cassette-receiving subassembly240 exploded upward from the inner cavity 210. The subassembly 240 isshown isolated in FIGS. 6A and 6B, and defines a heat exchangecassette-receiving cavity 242 (FIGS. 6B) on a front side thereof thatregisters with the similarly-sized opening 168 in the front panel 169when the subassembly is within the cavity 210. By this arrangement, aheat exchange unit of the present invention, such as a heat exchangeunit 54 of FIG. 2, or a heat exchange cassette as described below, canbe inserted through the front panel opening 168 and “plugged-in” to thecavity 242 within the subassembly 240.

As seen in both FIGS. 5G and 6A, a tubular skirt 244 depends from thesubassembly 240 and includes a lower flange 246 having a series ofthrough holes therein to enable attachment around the circular opening214 in the blower subhousing 212 (FIG. 5D). The skirt 244 thus providesa direct and contained pathway for the air blown upward by the blowerfor cooling the subassembly 240. Alternatively, the pathway for the airmay be reversed, with the blower pulling air downward through thesubhousing 212. The subassembly 240 further includes a plurality ofmounting brackets 248 that securely attach to a similar number ofsupport brackets provided in the cavity 210 of the control unit 150.

Heat Exchange Cassette-Receiving Subassembly

FIGS. 6A-6C further illustrate the various components of the heatexchange cassette-receiving subassembly 240 in several views and withseveral portions removed or exploded. With reference first to FIG. 6B,the subassembly 240 comprises, from top to bottom, an upper pressureplate 260, a pair of elongated side spacers 262, an upper guide assembly264, a lower guide assembly 266, a pump drive mechanism 268 attached toand depending downward from the lower guide assembly, a rear waterchannel assembly 270, a heater/cooler subsystem 272, and an air cooler274 disposed directly below the heater/cooler subsystem. In addition, afluid level measurement sensor module 276 is shown exploded in FIG. 6B,and is adapted to be mounted to the underside of the lower guideassembly 266.

The air cooler 274 comprises a hollow box-like structure having solidfront and rear walls, a circular opening (not shown) in the bottom wallto communicate with the interior of the tubular skirt 244, and a pair ofside walls with vents 278 that register with the vents 170 in thesurrounding control unit housing. In addition, the air cooler 274 isexposed to the underside of the heater/cooler subsystem 272. This isaccomplished by fastening a portion of the heater/cooler subsystem 272over the open-topped box of the air cooler 274, as will be described ingreater detail below with respect to FIG. 6C. In this manner, air blownthrough the tubular skirt 244 (either upward or downward) flows past theunderside of the heater/cooler subsystem 272. If the air is blownupward, it is redirected sideways through the vents 278 and 170 to theexternal environment. If the air is blown downward, it is pulled inthrough the vents 278 and 170 and is redirected downward through thefirst filter in the circular upper opening 214, and out through thesecond air filter 218 covering the square opening 220 to the externalenvironment. The air cooler 274 therefore acts as a highly efficientconvective heat sink for the heater/cooler subsystem 272. Of course,other types of heat sinks and other patterns of convective air coolingmay be used, and the present invention should not be considered limitedto the air blower 274 shown.

FIG. 6C shows the heater/cooler subsystem 272 exploded with an upperplate 280 separated from a lower plate 282 and between which a pluralityof thermoelectric (TE) modules 284 are sandwiched in thermal contactwith both. As mentioned previously, the lower plate 282 fastens over theopen top of the box-shaped air cooler 274. The TE modules 284 arepreferably discrete modules distributed over the surface of the lowerplate 282. In the exemplary embodiment illustrated, there are twelvesquare TE modules 284 distributed in rows and columns acrosssubstantially the entire area of the lower plate 282. The TE modules 284preferably function on the well known Peltier principal, wherein thesame TE modules may either heat or cool depending on the direction of DCcurrent through the units. All the TE modules described here arearranged so that current flows through each in the same direction.Therefore, merely by changing the polarity of the current flowingthrough the TE module the heater/cooler subsystem can be instantlychanged from a heater to a cooler or visa versa. The amount of heat orcold generated can also be adjusted by controlling the amount of currentflowing through the TE modules. Thus a very high level of control may beexercised by control of only one variable, the DC current supplied tothe TE modules.

The upper plate 280 provides a conductive heat transfer interfacebetween TE modules 284 and the heat exchange cassette inserted withinthe cavity 242, and tends to distribute the discrete temperaturedifferentials provided by the TE modules 284 over its surface. Thishelps to prevent localized heating or cooling of the heat exchangecassette, which may provoke an erroneous temperature measurement.Further, the upper plate 280 is manufactured of a suitably rigid metalhaving good thermal conductivity, such as anodized aluminum or othersuitable material. The rigidity of both the upper plate 280 and theupper pressure plate 260 are sufficient to resists bending from fluidpressurization of the heat exchange cassette positioned in the internalcavity 242.

With reference again to FIGS. 6A and 6B, connection of the variouscomponents of the subassembly 240 creates the aforementioned internalcavity 242 into which a heat exchange cassette of the present inventioncan be inserted. In the preferred embodiment, a cassette is provided asdescribed in greater detail below comprising a relatively thick bulkheadportion and a relatively thin heat external heat exchanger with theexternal heat exchanger sized to fit between the upper pressure plate260 and the upper plate 280 of the heater/cooler assembly 272. In thisregard, the lower guide assembly 266 includes a pair of upstanding sidewalls 290 a, 290 b each having guide slot 292 a, 292 b facing inwardtoward the other. The guide slots 292 a, 292 b are sized to receive theside edges of the external heat exchange unit such that the unit isreliably directed into the narrow gap defined between the upper pressureplate 260 and the upper plate 280. Although not shown, a micro-switch isdesirably provided in the slot 292 of one of the upstanding side walls290 to indicate when the heat exchange cassette has been fully insertedinto the internal cavity 242, and is engaged therein for properoperation of the system. Also not shown but well known in the relevantart, registration means such as pressure pins or balls and matingdetents may be provided in the control unit and cassette respectively toaid in the correct relative positioning between the cassette and thecontrol unit. The heat exchange cassette-receiving subassembly 240further includes a system for driving a pump provided in the heatexchange cassette. More specifically, as mentioned above with respect toFIG. 6B, and as shown in more detail in FIGS. 7A-7D, the pump drivemechanism 268 is attached to the underside of the lower guide assembly266 for powering a pump in the heat exchange cassette. As shown frombelow in FIG. 7C, the pump drive mechanism 268 preferably includes anelectric motor attached to the underside of the lower guide assembly 266and having an output shaft (not shown) engaged with a drive belt 300that, in turn, rotates a pump drive shaft 302 via a pulley 304, thedrive shaft being journaled to rotate within a vertical through bore inthe lower guide assembly 266. Other alternative methods of transferringrotational motion from the pump drive motor are clearly anticipated bythis disclosure and may include a series of gears between the electricmotor and the output shaft, a direct drive mechanism whereby theelectric motor directly engages the pump in the cassette, or othersimilar configurations.

With respect to FIGS. 7A and 7B, the upper end of the drive shaft 302 islocated within an irregular channel 306 formed in the top side of thelower guide assembly 266. The upper end of the drive shaft 302 presentsa drive gear 308. Although not shown, an exemplary heat exchangecassette of the present invention includes a downward projection thatfits within the channel 306 and includes a pump head gear 774 in FIG.15A that engages drive gear 308. A pair of idler hubs 310 a, 310 b mayalso be provided to engage the pump shaft idler wheels and position thepump head gear in engagement with the drive gear 308. A series ofrelated pins and bearings are shown in the drawings, but will not befurther explained with the understanding that a skilled artisan wouldunderstand the various functional and design alternatives.

FIGS. 7A-7D also illustrate a cavity 312 formed in the underside of thelower guide assembly 266. A series of through holes 314 extend betweenthe cavity 312 and the top side of the lower guide assembly 266. As seenin FIG. 7B, a transparent window 316 fits into a correspondingly-sizedrecess 318 and covers the holes 314. A fluid level measurement sensormodule 276 seen in FIGS. 6A and 6B fastens within the cavity 312 andincludes optical transmitters/sensors that are placed in registry withthe openings 314 and interact with the heat exchange cassette to providean indication of fluid level within the unit, as will be furtherexplained below.

Electronic Control Circuit of the Present Invention

As an alternative to the control system described in conjunction withFIGS. 3A-3B and the graph of FIG. 4, the controller may employ acascading PID control scheme. In such a scheme, a control board isprovided that may be divided into two sections: (a) a Bulk PID controlsection which takes input from the user (in the embodiment shown, RAMPRATE and TARGET TEMPERATURE) and input from the sensors on the patientrepresenting patient temperature, and calculates an intermediate setpoint temperature (SP1) and an output signal to the Working Fluid PIDcontrol; and (b) the Working Fluid PID control, that receives input fromthe Bulk PID control section and from a sensor representing thetemperature of the working fluid, and generates a signal that controlsthe temperature of the TE cooler by varying the power input to the TEcooler. The working fluid circulates in heat transfer proximity to theTE cooler, so the Working Fluid PID essentially controls the temperatureof the working fluid. In this way, the control scheme is able toautomatically achieve a specified target temperature at a specified RAMPRATE based on input from sensors placed on the patient and the logicbuilt into the controller. Additionally, this scheme allows the unit toautomatically alter the patient temperature very gradually the last fewtenths of a degree to achieve the target temperature very gently andavoid overshoot or dramatic and potentially damaging swings in theelectronic power to the TE cooler. Once the target temperature isachieved, the system continues to operate automatically to add or removeheat at precisely the rate necessary to maintain the patient at thetarget temperature.

Specifically, this is achieved as illustrated in FIG. 8. FIG. 8illustrates an exemplary electronic control circuit of the presentinvention specifically adapted for use in control unit 150 of FIG. 5A,but applicable to any control unit described herein. Some of theseelements correspond to elements identified previously, and thus, whereappropriate, reference numbers will be repeated for clarity. In general,the control circuit includes a control board having a number of logicalcomponents indicated within the dashed line 322, a user input 324, adisplay output 326, a plurality of sensors 328, a number of elements ofelectronic hardware indicated within the box 330, and a safety system332. The user inputs 324 and display outputs 326 were described abovewith respect to the control panel 160 of FIG. 5C. The two user inputs324 applicable to the control circuit in this embodiment are the targettemperature adjustment buttons 192 and cooling/warming rate adjustmentbuttons 194. The display outputs 326 applicable to the control circuitare the patient temperature display 174 and the alarm display 200, butmay include a number of other displays for various feedback to the user.A plurality of sensors 328 may be provided, including at least a sensor327 that senses the patient's actual body temperature and generates asignal represented by line 326, and a sensor 329 that senses thetemperature of the working fluid and generates a representative signal331. As stated previously, the working fluid may be, for example, salinethat is heated or cooled by passing in heat exchange proximity with a TEcooler 348 and then is circulated within a heat exchange catheter.

After the system is primed, a set point temperature (SP1) is determinedwith a set point calculator 334 using the target temperature and thedesire ramp rate as inputs. This set point temperature represents aninterim target temperature that the system will achieve at any giventime, for example 0.1° C. each 6 minutes, if the ramp rate is 1° C. perhour, starting with the initial patient temperature. This set pointtemperature is transmitted to a Bulk PID control section 336 of thecontrol board. The Bulk PID control 336 also receives input from thebody temperature sensor 327.

Based on the differential between the SP1 and actual body temperature,if any, the Bulk PID control 336 raises or lowers the temperaturespecified for the heat exchange fluid that will be circulated throughthe exchange catheter so as to induce a change to the patienttemperature at the specified ramp rate. That is, a value for the desiredworking fluid temperature, or a second set point temperature (SP2), istransmitted to a Working Fluid PID control unit 338 as illustrated at337. The Working Fluid PID control unit 338 also receives input from thetemperature sensor 329 for the working fluid as illustrated at 333. TheWorking Fluid PID control unit 338 compares the sensed working fluidtemperature with the desired working fluid temperature transmitted fromthe Bulk PID control to determine a differential, if any. Based on thisdifferential, the Working Fluid PID control 338 transmits a digitalsignal as illustrated at 340 to an “H-Bridge” polarity switching unit342, which directs power of an appropriate magnitude and polarity to theTE cooler 348 to cause the TE cooler to be heated or cooled toward thedesired temperature. This, in turn, heats or cools the working fluid asthe system operates to circulate the working fluid in heat exchangeproximity to the TE cooler.

The polarity switching unit 342 receives power from a source 344 andtransforms that power to the appropriate magnitude and polarityrequested by the Working Fluid PID control unit. Between the powersource and the polarity switching unit is a safety relay 346 actuated bythe safety system 332 that will, in the absence of a safety issue,transmit the power from the power source 344 to the polarity switchingunit 342. If the safety system 332 is aware of a safety issue, forexample if a low fluid level is sensed, it may direct the safety relay346 to open and prevent power from the power supply 344 from beingdirected to the TE cooler 348. In the absence of any safety issue,however, the polarity switching unit 342 transmits the power to theheater/cooler unit 348 in accordance with the request from the WorkingFluid PID control unit. Various subsystems of the present inventionprovide input to the safety system 332, and will be described below whenintroduced.

The control circuit includes logic that permits rapid heat exchange whenthe target temperature and the sensed body temperature are relativelyfar apart, and which slows down the rate of heat exchange as the sensedbody temperature nears the target temperature. As the sensed patienttemperature and the SP1 become very close, the Bulk PID will dictateonly a very small change in the working fluid temperature, and thus therate of change will become smaller and smaller as the SP1 becomes veryclose to the sensed patient temperature until the rate of change isessentially non-existent. In this way, the patient temperature verygently is heated or cooled the last few tenths of a degree, avoidingovershoot or dramatic swings from heating to cooling when the bodytemperature is at the target temperature. As the input TARGETTEMPERATURE is reached, the SP1 and the TARGET TEMPERATURE areessentially the same, and the system operates to set the power to the TEcooler at a level that maintains the necessary working fluid temperatureto hold the patient temperature at the TARGET TEMPERATURE. In this way,the system will work to maintain a target temperature with the workingfluid maintained at just the right temperature to add or remove heat atthe precise rate necessary to maintain that target temperature asessentially a steady state.

The Working Fluid PID control 338 samples its respective inputs at arate of 10 times a second and updates the output to the polarityswitching unit 342 at a rate of once every second, and thus the trendsof changing patient temperature are constantly monitored and adjusted.The Bulk PID control 336 samples its inputs at the same rate, and thus anew target temperature or a new ramp rate can be specified by the userwith nearly instantaneous system response.

A First Exemplary Heat Exchange Cassette

Suitable heat exchange cassettes for use in the invention are describedin U.S. Patent Application 60/185,561 incorporated in full herein byreference. Such catheters are generally described below.

FIG. 9 schematically illustrates an exemplary heat exchange cassette 400of the present invention shown adjacent to a receiving opening 402 in acontrol unit 404. The control unit 404 may be configured like element 50described above with reference to FIG. 2, or like element 150 withreference to FIGS. 5-8. Consequently, the control unit 404 includes aheater/cooler mechanism (not shown in FIG. 9), a pump drive mechanism406 (schematically shown), a controller processor, and a manual inputdevice (also not shown in FIG. 9). The pump drive mechanism 406 includesa drive gear 408 and a pair of idler wheels 410, similar to theembodiment shown in FIGS. 7A-7D.

FIG. 9 further schematically illustrates exemplary placement of anoptical beam source 412 and optical beam sensor 414 used to determine afluid level within the heat exchange cassette 400, as will be explainedfurther below. Furthermore, exemplary placement of a valve actuationsystem 416 including, at least, a linear actuator 418 and push rod 420is shown. Finally, it will be appreciated by one skilled in the art thatthe various advantageous features described above with reference toFIGS. 2 and 5-8 may be ascribed to the control unit 404 of FIG. 9.

FIG. 9 illustrates certain aspects of the overall heat exchange cathetersystem of the present invention, as described above with respect to FIG.2, including a heat exchanger 422 on the distal end of an in-dwellingcatheter 424 through which a heat exchange fluid may be circulated viaan inflow line 426 and outflow line 428. The fluid inflow and outflowlines 426, 428 are typically of a flexible compressible material such aspolyvinyl chloride or other suitable flexible compressible tubingmaterial, and are fluidly connected to a bulkhead 430 of the heatexchange cassette 400. A fluid supply bag 432 supplies heat exchangefluid for priming the system via a supply line 434 which can be closedthrough the use of a stop cock or pinch clamp 436. Bag size is notgenerally critical but has a typical capacity of about 250 ml. Thedisposable heat exchange cassette 400 can be packaged with or separatelyfrom the heat exchange catheter 424.

The heat exchange cassette 400 comprises the aforementioned bulkhead 430to which an external heat exchanger 440 is coupled via a cover plate442. As mentioned above, the external heat exchanger 440 issubstantially flat and thin so as to fit within a narrow slot or gapprovided within the control unit 404 and be sandwiched between aheater/cooler plate and a pressure plate. The bulkhead 430 is somewhatthicker and is provided with a handle 444 to facilitate insertion andremoval from the control unit 404. Additionally, the bulkhead 430 dockswithin an outer portion of the opening 402 such that the pump drivemechanism 406 engages a pump head therein. Exemplary details of the pumphead will be provided below. (It should be noted that the FIGS. depicttwo different embodiments of the bulkhead. The bulkhead shown in FIG. 9is described in greater detail with respect to FIGS. 10B, 13A-13E and14A-14E.)

It should also be reiterated that the control unit 404 comprises are-usable component of the entire system, while the heat exchanger 440,catheter 424, and fluid supply 432 comprise disposable components.Indeed, in a preferred embodiment, all the components except for thecontrol unit 404 are packaged together in a sterile pre-assembled unit.This arrangement enables the medical staff to set up the entire systemby simply opening up the sterile package, “plugging-in” the heatexchange cassette 400 into the control unit 404, and introducing thecatheter 424 into the appropriate location in the patient. After theprocedure is over, everything but the control unit 404 is disposed of.

With reference now to FIGS. 10A and 10C-10D, an exemplary heat exchangecassette 400 a of the present invention will be described. As describedabove, the exchange unit 400 a includes a bulkhead 430 a, an externalheat exchanger 440 a, and a cover plate 442 a. The bulkhead 430 aincludes a reservoir section 450 and a pump section 452 shown explodedin FIG. 10A, and coupled together for fluid communication in FIG. 10B.

The cutaway plan view of FIG. 10B shows a number of flow arrows thatindicate the flow path of heat exchange fluid through the bulkhead 430 aand external heat exchanger 440 a. Beginning from an external fluidsource 454, such as the fluid bag 432 shown in FIG. 9, an inlet line 456primes the reservoir section 450, and fluid is then pumped to the rightin the drawing through an L-shaped outlet channel 458 (FIG. 10C) andinto an inlet 459 of the pump section 452. The outlet of the pumpsection 452 diverges into two channels, one of which leads to theexternal heat exchanger 440 a, and another of which leads to the flowline 460 that supplies the in-dwelling catheter. Selection of which ofthe pump section outlet channels receives fluid will be described ingreater detail below. Suffice it to say that heat exchange fluid firstprimes the catheter flow lines, and then primes the external heatexchanger 440 a. Fluid flows through an outlet 462 on the upper side ofthe pump section 452 into the external heat exchanger 440 a and into aplurality of serpentine pathways defined therewithin. After passingthrough the heat exchanger 440 a, fluid flows back into an inlet 464 ofthe reservoir section 450.

With reference still to FIGS. 10A and 10C-10D, but with particularreference to the perspective view of FIG. 10C, the reservoir section 450comprises a lower container 470 that includes, as a top wall, an uppercover plate 472 closely received in a stepped rim of the container andis fastened thereto by a biocompatible adhesive. The container 470defines a fluid cavity 474 therewithin which receives fluid from twosources: a supply inlet 476 to which the external fluid source conduit456 attaches, and the inlet 464 connected to the interior of theexternal heat exchanger 440 a. The L-shaped channel 458 provides a fluidoutlet located at the end of the reservoir section 450 fluidly connectedto the pump inlet 459. Located at the same end of the reservoir as theL-shaped channel is a damping chamber 478 that is not open to thereservoir. A compressible material 480, such as a block of foam, fitsthrough a projecting collar 482 and into the damping chamber 478. Thefunction and advantage of such a damping chamber 478 will be describedfurther below.

The cover plate 472 seals around the edge of the container 470 to createthe fluid cavity 474, but is provided with one or more vent holes 484fitted with hydrophobic gas-permeable vents permitting the release ofair from within the cavity. The vent holes 484 permit air to bedisplaced from within the container 470 when fluid is introduced thereinduring a system priming operation, without permitting escape of anyfluid therefrom. The pore size on the vent holes 484 is small enough toprevent the entrance of any contaminants such as microbes, thusmaintaining the sterility of the fluid that is being circulated throughthe catheter in the patient's body. First and second prisms 486 a, 486 bare also located within the container 470 as part of a fluid leveldetection system, to be described further below. The location of theprisms in this embodiment are adjacent the wall of the damping chamber478, but on the embodiment shown in FIG. 9 are at the other end of thereservoir, and are attached as shown in FIG. 13E at 590 a, 590 b. As oneof skill in the art will readily recognize, the location of the prisms,and the function whether vertical or horizontal is a matter of designchoice, and requires concomitant changes in the location of the opticalbeam sensors 412, 414 in the control unit.

As seen in FIG. 10B, the pump section 452 includes a rotating-type pumphead 490 defined within a quasi-cardioid shaped cavity 492. The pumphead 490 includes a rotor 494 and a movable vane 496, and rotates on ashaft (not numbered) that is driven by an external source, such as thepump drive mechanism 406 seen in FIG. 9. The pump head 490 is desirablyable to pump fluid through the system at pressure in excess of 35 psiand, more preferably, is able to rapidly achieve and maintain apredetermined pressure, for example 40 psi. Specific details of the pumphead 490 will be provided below with respect to FIGS. 15-16, it beingunderstood that the rotating-type pump can be a vane pump as shown, animpeller pump, or a gear pump. Furthermore, with some modification, thepresent system can utilize other types of fluid pumps, such as diaphragmpumps or peristaltic pumps.

The pump section 452 also has a flow-through channel 497 having a fluidcoupling inlet means 498 that leads from the catheter directly to theoutlet 462 leading to the external heat exchanger 440 a. As seen inFIGS. 10B and 10D, a diverging pump outlet channel 499 is in fluidcommunication with a fluid coupling outlet to the catheter 460, and alsoto the pressure dampening chamber 478. The pressure damping chamber maybe filled with, for example, a block of compressible material 480 in afluid path that is parallel with the fluid flowing to the catheter.Fluid from the pump flowing to the catheter is thus exposed to thecompressible material 480 within the dampening chamber 478, and as fluidcontacts the compressible material 480, the material compresses slightlyand then returns to its original configuration, and in doing so acts asa cushion to absorb minor pressure fluctuations in the fluid that mayresult from the action of the pump. The compressible material thus hasthe effect of dampening pressure pulses in the fluid flow to thecatheter.

Suitable examples of the compressible material include a block of foam,encapsulated foam such as polyethylene foam encased in a polyethylenefilm, foam enclosed within a sealed plastic pouch, foam coated with orimpregnated with plastic or silicone, gas encapsulated within a flexiblepouch such as a polyethylene balloon, and so forth.

Exemplary External Heat Exchanger

The external heat exchanger shown as 440 in FIG. 9 and 440a in FIG. 10Acan be any combination of one or more structural and compliant memberssuch that the overall configuration of the external heat exchanger isadapted to mate with the opening provided in the control unit 404 a. Ina preferred embodiment, as seen in the cross sections of FIGS. 11A and11B, the structural member comprises a planar back plate 500 and thecompliant member comprises a layer 502 of flexible, thermally conductivematerial. The compliant layer 502 is sealed to the back plate 500 in apattern which forms a serpentine flow channel 504 therebetween, as seenin FIG. 10A. The flow channel 504 includes a fluid inlet orifice 506provided with a flow fitting 508, and a fluid outlet orifice 510provided with an identical flow fitting 512. The flow fittings 508 and512 are seen in perspective in FIGS. 12A and 12B.

The back plate 500 is typically stiff and made of a high densitypolyethylene and is generally about 0.762 mm (0.030 inches) thick. Thethinner compliant layer is shown in this embodiment as being sealed in aserpentine pattern to the back plate by fusing, such as by heat sealingor other suitable technique to permanently adhere the two layerstogether. The pattern of heat sealing creates a serpentine pathwaycomposed of sealed portions 514 separating the continuous serpentineflow channel 504 or, alternatively, a plurality of flow channels.

The winding flow channels 504 form a pathway which causes the heatexchange fluid to flow back and forth adjacent to and in heat transferrelationship with the heater/cooler device within the control unit 404a, and ensures that the fluid circulates proximate to the heatheater/cooler device for a sufficient amount of time to allow foradequate heating or cooling of the fluid. The present invention also mayutilize sealed portions that are not continuous, as long as the sealedportions are configured so as to create channels that permit fluid flowthrough the external heat exchanger 440 a. In addition, the externalheat exchanger can be configured to have a V-shaped leading edge 516that acts as a guide to facilitate placement into the control unit 404.

The thinner compliant layer 502 is generally about 0.102-0.203 mm(0.004-0.008 inches), and is typically a low density polyethylenematerial that is slightly elastomeric or compliant so that whenpressurized heat exchange fluid flows into the legs of the serpentinechannels 504, they bow out slightly as may be seen by comparing FIG. 11A(uninflated) and FIG. 11B (inflated). Since the back plate 500 andthinner compliant layer 502 are both polyethylene, they weld togethereffectively by means of heat fusion or ultrasonic welding. However, thebulkhead 430 a is not the same material, and therefore the external heatexchanger is generally sealed to the bulkhead by other means, such as bya mechanical pressure seal.

As seen in FIG. 10A, the external heat exchanger 440 a is provided withan extended attachment 520 that is sealed to the bulkhead 330. Theextended attachment 520 has three sections distributed across thebulkhead 330; a first flap section 522 a, a cutaway section 522 b, and asecond flap section 522 c. One or more vent holes 524 are cut into thefirst flap section 142 to allow air to vent from the correspondingnumber of hydrophobic gas permeable vents 484 in the reservoir coverplate 472, as was described above. While a plurality of vent holes 524is shown in the embodiment of FIG. 10A, any suitable shape or number ofholes will suffice, for example a single vent hole is shown in theembodiment of FIG. 13A, infra.

As mentioned, each of the orifices 506, 510 opening to the serpentinechannels 504 is provided with a fitting 508, 512 that allows fluid toflow into the space between the thin compliant layer 502 and the backplate 500. When heat exchange fluid is pumped into the inlet orifice 506through the first fitting 508, it winds its way along the serpentinepath to the outlet orifice 510 and then enters the bulkhead through thesecond fitting 512. The entire external heat exchanger 440 a is placedin thermal contact with a heater/cooler within the control unit 404,such as the heat exchange surface of a thermoelectric cooler or a numberof TE cooler modules in contact with a thermal plate (as shown in FIG.6C). The thinner compliant layer 502 is positioned against the heatexchange surface so that the temperature of heat exchange fluid may becontrolled by controlling the temperature of the surface and pumpingfluid through the external heat exchanger.

The fittings 508, 512 are secured within the inlet and outlet orifices506,510 by virtue of their particular construction, as illustrated inFIGS. 12A and 12B. Each fitting 506, 510 has a central channel 530, abase plate 532, a plurality of spacer protrusions 534 on the lowersurface of the base plate, and a nose 536 projecting in the oppositedirection from the base plate 532. The embodiment of FIG. 12Billustrates four such protrusions but the invention contemplates havingfewer or more than four protrusions. When the fitting 506 is placed inthe external heat exchanger 440 a, the nose 536 projects through theinlet orifice 506, and the base plate 532 is tightly positioned betweenthe compliant layer 502 and the back plate 500. The spacer protrusions534 space the base plate 532 away from the back plate 500 of theexternal heat exchanger. At the outlet orifice 510, fluid containedwithin channels 504 passes between the protrusions, through channel 530,and then into bulkhead 430 a. Similarly, fluid returning from the heatexchange catheter enters the heat exchange channels 504 through thecentral channel 530 in fitting 506, and passes between the protrusions534. Two O-rings, such as flexible rubber washers, can be positionedaround the periphery of the nose 536 of each fitting 506, 510 betweenthe compliant layer 502 and the bulkhead 430 a. The noses 536 of eachfitting 506, 510 are sized to be inserted into the associated outlet 462and inlet 464 of the bulkhead 430 a.

A Second Exemplary Heat Exchange Cassette

FIGS. 13A-13E illustrate a second exemplary heat exchange cassette 400 bthat is in many ways similar to the first-described heat exchangecassette 400 a, but has a bulkhead assembly that includes a feedblocksection and pressure valve as described below. As in the earlierembodiment, the exchanger 400 b includes a bulkhead assembly 430 bcoupled to an external heat exchanger 440 b through the use of coverplate 442 b. The bulkhead assembly 430 b includes a reservoir section550 a pump section 552 and a feedblock section 554 disposedtherebetween. These three sections can be independent and discrete unitsthat are coupled together, as seen in FIG. 13A, or may be defined withina single unit. The bulkhead section(s) can be machined, molded, or cast,and are typically made of the durable, lightweight material such asplastic or PLEXIGLAS.

With reference to the perspective views of FIGS. 13A and 13E, the hollowreservoir section 550 has an elongated rectilinear shape with a pair ofcollars on one longitudinal end facing the feedblock section 554:namely, a fluid outlet collar 560 defining a reservoir outlet channel561 and a pressure regulator collar 562. These two collars securelyengage two collars of slightly smaller size on the juxtaposed end of thefeedblock section 554; specifically, as seen in FIG. 14A, a fluid inletcollar (not shown) and a pressure sensing chamber collar 564. Thefeedblock section 554 is also a hollow, generally rectilinear housingand includes, on the side facing the pump section 552, an inlet collar566 leading to an inlet conduit 568, a first outlet collar 570 openingfrom a first outlet conduit 572, and a second outlet collar 574 openingfrom a second outlet conduit 576. A series of O-rings 578 are sized tofit around each of these collars 566, 570, 574 and ensure fluid tightseals between the collars and associated openings formed in thejuxtaposed side of the pump section 552.

a. Exemplary Reservoir Section

With reference still to FIGS. 13A-13E, but with particular reference tothe perspective view of FIG. 13E, the reservoir section 550 comprises alower container 580 that includes, as a top wall, an upper cover plate582 closely received in a stepped rim of the container which may befurther affixed with adhesive or heat welding or other acceptablefastening method. The container 580 defines a fluid cavity 584therewithin which receives fluid from a single source: an inlet 586connected to the interior of the external heat exchanger 440 b. Thecover plate 582 seals the fluid cavity 584 around the edge of thecontainer 580, but is provided with one or more vent holes 588 fittedwith hydrophobic gas-permeable vents permitting the release of air fromwithin the cavity during a priming operation.

First and second prisms 590 a, 590 b are also located within thecontainer 580 adjacent a transparent bulkhead material or window 591 aspart of a fluid level detection system. As seen in FIG. 13D, the lowercontainer 580 can be configured so as to have an indented or sloped area592 in the base. The sloped or indented area defines a fluid channel orsump from the interior fluid cavity 584 of the reservoir adjacent theprisms 590 a, 590 b to the fluid outlet 561. In this way the fluidopening leading to the reservoir outlet channel 561 is at approximatelythe same elevation as the prisms 590 a, 590 b which will thereforeassure fluid to the pump even if the level of fluid at the prisms isquite low. As will be discussed below, the prisms are safety systems fordetecting low fluid level, a potentially dangerous condition, and theindented area 592 adds extra insurance that a low fluid level will bedetected before an absence of fluid to the pump becomes a problem.

As seen in FIG. 13E, a pressure regulator shaft 598 mounts in the fluidreservoir cavity 584 through a mounting flange 600 extending into thecavity from one of the side walls of the container 580. In oneembodiment, the pressure regulator shaft 598 includes threads which matewith internal threads provided in a through hole 602 in the flange 600.A reference spring 604 is biased between the shaft 598 and a diaphragm606. The diaphragm 606 may be a membrane, for example, acloth-reinforced silicone membrane. Because of the presence of thehydrophobic gas permeable vents 588, the pressure on the reservoir sideof the diaphragm 606 is essentially atmospheric pressure plus thepressure applied by reference spring 604. The pressure of referencespring 604 may be adjusted by advancing or retracting the shaft 598within the threaded hole 602, which in turn adjusts the amount of springforce applied against the diaphragm. A pressure plate 608 is interposedbetween the diaphragm 606 and the reference spring 604 to more evenlydistribute the pressure of the spring to the reservoir side ofdiaphragm. Further specifics of this exemplary pressure regulatingmechanism of the present invention will be described below.

b. Cover Plate

As with the earlier described heat exchange cassette 400 a, the externalheat exchanger 440 b of FIG. 13A includes an extended attachment flange610 that is secured to the upper side of the bulkhead assembly 430 b bythe cover plate 442 b. Preferably, a mechanical seal is formed betweenthe attachment flange 610 and the bulkhead assembly 430 b by virtue of anumber of fasteners (not shown) extending between the cover plate 442 band the bulkhead assembly. The cover plate 442 b includes a handle 612for ease of manipulation of the heat exchange cassette 400 b.

The cover plate 442 b further includes a plurality of apertures andgrooves that interact with the bulkhead assembly 430 b, and also withthe re-usable control unit of the present invention, such as theexemplary control unit 404 of FIG. 9. For example, an elongated aperture614 registers with a similarly shaped aperture 616 in the attachmentflange 610, both apertures permitting passage of air from the reservoirsection vents 588. The cover plate 442 b further has a priming valveaperture 618 that permits access to a flexible diaphragm of thefeedblock section 554, as described below. Furthermore, the cover plate442 b is configured to have one or more indicators to alert the userthat the heat exchange cassette is in the correct position foroperation. For example, the cover plate may have a slot that operates todepress a switch on the control unit to indicate proper placement, suchas a switch in the receiving opening 402 of the exemplary control unit404 of FIG. 9. Similarly, the cover plate 442 b may have slots 620,leading to depressions 622 that receive biased detents such as springloaded bearings on the control unit. When the heat exchange cassette 400b is being positioned within the control unit, the detents will beguided along the slots 620, and once the unit is fully inserted thedetents will cam into the depressions 622 with an audible click toinform the user that placement is complete. As one of skill in the artwill understand, a more secure positive locking arrangement maybe,provided, although as will be described below, pressurization of theexternal heat exchanger 440 b serves to hold the heat exchange cassette400 b tightly within the re-usable control unit.

c. Fluid Pathway Through Second Heat Exchange Cassette During AutomaticPrime

Prior to a detailed description of the sections of the bulkhead assembly430 b, fluid flow through the heat exchange cassette 400 b will begenerally explained. When the external fluid source has been attached tothe feedblock 554, the system is initially filled with fluid and purgedof air before insertion into a patient. This process is called priming.The priming is done automatically by the cassette in conjunction withthe control unit depicted in FIG. 9. The control unit initiallyactivates a priming push rod 420 that depresses a flexible membrane 672on the coverplate above the valve actuating rod 680. This positions thevalve in the feedblock to the “prime” position (FIG. 14E) so that fluidfrom the fluid source enters a fluid fill reservoir 682 a, and isdirected toward the pump through pump feed line 640. The feed line fromthe reservoir is closed and fluid enters from the fluid bag, to thepump, thence through the pressure regulating chamber, the catheter, backinto the heat exchange unit, through the serpentine path, and into thereservoir. As the reservoir fills, the air that is displaced is expelledthrough the hydrophilic valves. Once the reservoir is full, the fluidlevel detectors signal the control unit that the reservoir is full, andthe prime valve is deactivated, so that push rod 420 withdraws, flexiblemembrane 672 relaxes, and the valve actuating rod, 680, which is biasedby spring 678 to the upward position, returns to the “run” position. Inthis position, the priming valve is positioned in the run position (FIG.14D) and fluid is pumped in a closed circuit from the reservoir, throughthe pump, through the pressure regulating chamber, through the catheter,back into the heat exchange unit across the TE cooler through theserpentine path, and into the reservoir.

Referring now to FIGS. 13A-13C, a number of fluid flow arrows areindicated in FIG. 13B. An external fluid source 630 attaches to a fillport 632 leading to a fill channel 634 in communication with a centralchamber 636 of the feedblock section 554. The fluid outlet collar 560 ofthe reservoir section 550 also directs fluid to the central chamber 636via an internal channel 638 in the feedblock section. A further internalchannel 640 of the feedblock section 554 provides an outlet from thecentral chamber 636 leading to the first outlet conduit 572 definedwithin the first outlet collar 570, seen in FIG. 14A, and, ultimately,to the pump section 552.

Initially the system is primed as described in the next section. Thisfills the reservoir, the catheter, and the external heat exchanger withfluid and expels the air in the system. The system is then in the RUNcondition, whereby fluid is pumped in a closed circuit in approximatelythe following pathway. The pump section 552 includes a rotary-type pumphead 642 that propels fluid through an outlet channel 644 and back intothe pressure regulating chamber 646 in the feedblock section 554 via theinlet conduit 568 within the inlet collar 566. The pressure regulatingchamber 646 has an outlet channel 648 and outlet port 650 to which acatheter inflow line 652 (FIG. 13B) couples. The fluid is pumped throughthe heat exchange catheter from the outlet channel. After passingthrough the heat exchange catheter, fluid returns through an outflowline 654 that couples to an inlet port 656 (FIG. 13C). The return heatexchange fluid then passes through a relay channel 658 and passes out ofthe feedblock section 554 through the second outlet conduit 576 withinthe second outlet collar 574. Fluid then passes through a flow throughchannel 660 within the pump section 552 leading to a bulkhead outlet662, as also seen in FIG. 13A.

The bulkhead outlet 662 leads to one or more internal flow channelsprovided within the external heat exchanger 440 b. As with theearlier-described embodiment, the heat exchanger 440 b may be anycombination of one or more structural and compliant members such thatthe overall configuration is adapted to mate with the opening providedin the control unit 404 a. For instance, the heat exchanger 440 b may beconstructed as seen and described with respect to the cross sections ofFIGS. 11A and 11B. Namely, the heat exchanger 440 b may include a rigidback plate 500 and a layer 502 of flexible, thermally conductivematerial sealed to the back plate 500 in a pattern which forms aserpentine flow channel 504 therebetween. The aforementioned flowfittings 508 and 512 seen in FIGS. 12A and 12B are also desirably usedto facilitate inflow and outflow from the serpentine flow channel 504.

After passing through the flow channel 504 within the heat exchanger 440b, fluid enters the reservoir cavity 584 through the bulkhead inletorifice 586. And finally, from the reservoir section 550, fluid passesthrough the outlet collar 560 back into the central chamber 636 of thefeedblock section 554.

Alternatively, the system of the present invention can be passivelyprimed, and the fluid level maintained without resort to a switchingvalve as described above. That is, a fluid supply bag may be attached soas to drain by gravity to prime the system. At the same time there is nobackflow valve and the bag accepts excess fluid if, for example, thefluid expands when heated. If the heat exchange balloon leaks and thecircuit starts to empty, the bag will continue to fill the system untilempty and then a fluid level detector will sense the low level, sound analarm and shut the flow off. A small fluid bag (e.g., 50 cc's maximum)is desirable so that if there is a leak a minimum amount will be pumpedinto the patient. Such a small volume is not considered a medical riskto the patient.

d. Exemplary Feedblock Section

FIGS. 14A-14E illustrate the component parts of the exemplary feedblocksection 554 that provides one embodiment of a priming valve and a fluidregulator for the heat exchange catheter system of the presentinvention. As mentioned, the central chamber 636 has a first inlet influid communication with an external fluid source 630, a second inlet influid communication with the reservoir section 554, and an outlet influid communication with the pump section 552. A priming valve 670mounted within the central chamber 636 regulates flow into the centralchamber from either of the first and second inlets, depending on thefluid level within the reservoir section 550. The priming valve 670includes, from top to bottom in FIG. 14A, a flexible membrane 672, anannular guide disk 674 having a central orifice 675, a valve member 676,a valve spring 678, and a valve stem 680. As seen in FIGS. 14D and 14E,these components are arranged within the central chamber 636, whichactually comprises a series of three gradually smaller steppedsubchambers 682 a, 682 b, 682 c.

The solid flexible membrane 672 covers the central chamber 636, and moreparticularly, seats within a counter bore 684 and is fastened therein,such as with adhesive. A push rod, such as the push rod 420 in thereceiving opening 402 of the control unit 404 seen in FIG. 9, ispositioned to pass through the priming valve aperture 618 in the coverplate 442 b and displace the flexible membrane 672 downward which, inturn, displaces the valve member 676 downward, as seen in FIG. 14E. Thepush rod 420 is desirably not contained in the heat exchange cassette400 b, and may be manually triggered or automatically controlled such asby the valve actuation system 416 of FIG. 9. The push rod 420 may act,for example, by means of the linear actuator 418 displacing the push roddownward upon a signal from the processor of the control unit 404,triggered by full insertion of the heat exchange cassette 400 b into thereceiving opening 402 of the control unit 404.

Once the valve member 676 is displaced downward, the aforementioned fillchannel 634 (FIG. 13B) brings fluid from the external fluid source 630to the upper, largest subchamber 682 a. The guide disk 674 seats againsta shoulder 686 at the bottom of the upper subchamber 682 a that definesa transition between the upper subchamber and the middle subchamber 682b. The middle subchamber 682 b opens to the outlet channel 640, and alsosteps to the smaller lower subchamber 682 c. The lower subchamber 682 c,in turn, receives fluid from the reservoir section 550 via the inletchannel 638. The rigid valve stem 680 is fixedly position within acavity in the floor of the lower subchamber 682 c, and extends upwardinto the upper subchamber 682 a. The valve member 676 includes aninternal cavity 688 that receives the upper end of the valve stem 680 soas to permit relative linear movement therebetween. The valve spring 678surrounds the valve stem 680 and is placed into compression between thevalve member 676 and floor of the lower subchamber 682 c.

The valve member 676 has a lower annular flange 690 extending outwardfrom concave shoulders that receive and seat a pair of O-rings 692. Thevalve member 676 translates linearly along the valve stem 680 such thatthe O-rings 692 alternately contact the underside of the guide disk 674(FIG. 14D), and the floor of the middle subchamber 682 b (FIG. 14E). Thespring 678 normally biases the valve member 676 upward along the valvestem 680 such that the upper O-ring 692 seals against the underside ofthe guide disk 674. In this default position, seen in FIG. 14D, fluidflows from the reservoir section through the inlet channel 638, lowersubchamber 682 c, middle subchamber 682 b, and through the outletchannel 642 toward the pump head 552. Alternatively, during priming ofthe system, the push rod 420 is displaced downward, as seen in FIG. 14E,displacing the valve member 676 downward such that the lower O-ring 692contacts and seals against the floor of the middle subchamber 682 b. Inthis mode of operation, fluid flows from the fill channel 634 into theupper subchamber 682 a, through an annular space between the valvemember and the central orifice 675 of the guide disk 674, through themiddle subchamber 682 b, and through the outlet channel 642 toward thepump head 552.

e. Exemplary Pressure Regulator

A pressure regulator valve to regulate the pump output pressure isdesirable. It may also be seen that such a pressure regulator mayfunction to damp any pressure variations, such as vibrations in thefluid line generated by the pump. There are number of ways of regulatingpressure, including the aforementioned damping chamber in the embodimentof the invention illustrated in FIGS. 10A-10D. In the heat exchangecassette 400 b of FIG. 14A, the feedblock section 554 may include anexemplary pressure regulation system comprising a spring loadeddiaphragm that flexes to relieve pressures above a threshold value toensure that the heat exchange catheter is provided with heat transferfluid at a relatively constant pressure. In a third embodiment, describebelow, there is no pressure regulator in direct contact with the workingfluid under pressure, but instead the current of the pump motor ismonitored and maintained at a constant value. Those of skill in the artwill understand that these are not the only types of pressureregulators, and a particular type utilized may be selected based oncost, weight or size constraints, design considerations, or the like.

In one embodiment of a pressure regulator valve shown in FIG. 14B, theoutlet of the pump is fluidly connected to the inlet of the pressureregulator chamber 646. The pressure of the fluid at the pump output mayvary somewhat depending on wear and fluid temperature, and may be, forexample, 45-54 psi. As mentioned previously with respect to FIG. 13E, aportion of the pressure regulator of a second embodiment resides withinthe reservoir chamber 684 and includes the pressure regulator shaft 598mounted for linear adjustment within the flange 600, and the referencespring 604 biased between the shaft and the diaphragm 606.

A push rod 700 attaches to the right side of the diaphragm 606 andextends through a throttle chamber 702. The throttle chamber 702 has acloverleaf cross-sectional configuration in the form of a centralthrottle aperture 704 surrounded by four lobes 706, as may best be seenin FIG. 14C. The push rod 700 extends to the right and through athrottle aperture 708. A counter spring block 710 is mounted across theface of the aperture 708 and is biased toward the push rod 700 by meansof a counter spring 712. In the default position, the block 710 isbiased against the open aperture 708 to create a fluid-tight sealbetween a sensing chamber 714 and the regulator chamber 646.Alternatively, if the pressure applied against the diaphragm 606 by thespring 604 and the pressure in the reservoir cavity 584 is sufficient todeform the diaphragm 606 toward the sensing chamber 714, the push rod700 forces the counter-spring block 710 away from the throttle aperture708. This movement opens a throttle gap through which fluid may flowbetween the regulator chamber 646 and the sensing chamber 714. Becausethe throttle gap is relatively narrow, there is a pressure drop as fluidflows therethrough.

In practice, the reference spring 604 is adjusted so that the pressureagainst the diaphragm 606 and thus against the push rod 700 is, forexample, 43 psi. When the pressure in the regulator chamber 646 isgreater than 43 psi, it forces the counter spring block 710 closer tothe throttle aperture 708, thus narrowing the throttle gap. Thisfunctions to automatically adjust the throttle gap so that the pressuredrop across the throttle gap is the same as the excess pressure betweenthe fluid in the regulator chamber 646 and the pressure set by thereference spring 604 against the diaphragm 606, which is, in theexample, generally 43 psi. This acts to regulate the pressure of thefluid in the sensing chamber 714 to almost 43 psi. The fluid exits thesensing chamber through outlet 648 (FIG. 13C) and thence to the catheterinflow line 652 (FIG. 13B). In this way fluid at a relatively constantpressure is supplied to the catheter.

f. Indirect Method of Fluid Flow Control Using Motor Current

As mentioned above, controlling the pressure and/or flow rate of theheat exchange medium through the heat exchange catheter may beaccomplished by regulating the speed of the pump based on the backpressure of the fluid being pumped. Alternatively, conventional flowmeters may be provided within the fluid flow lines. However, each ofthese conventional systems presents an additional cost, and may besubject to failure or error. In addition, such monitoring elementsdesirably would be designed not to contact fluid directly so as to avoidpotentially contaminating the fluid. Non-contact flow and pressuresensors typically involve infrared or ultrasonic devices, which, alongwith the associated hardware to interpret the measurements, can beexpensive and subject to failure in use. Consequently, it may bedesirable to eliminate the pressure regulator valve, pressure regulatorchamber and sensing chamber from the cassette design. In that instance,another means of insuring constant pressure and providing for smoothfluid flow can be incorporated into the cassette design.

Although the present invention encompasses conventional means formonitoring the flow rate or pressure of the heat exchange medium, apresently preferred means is to monitor the current flow through thepump drive motor. The torque developed by an electric motor is directlyproportional to the current supplied to that electric motor. Where, asin the pump described below, friction within the pump in negligible sothat the torque generated by friction does not vary significantly withpump speed, the fluid pressure developed by a rotating pump vane such asthat described below is directly proportional to torque supplied by theelectric motor operating the pump. (Another way of describing thepressure developed by the pump is back pressure developed by thesystem.) Therefore by controlling the current supplied to the electricmotor at a constant amount regardless of the speed (rpm) developed bythe motor, the pressure output of the pump would be relatively constant.This pressure regulation to a constant current is achieved with a simpleamplification feedback which is well known to those in the art and willnot be described in greater detail here.

Suffice it to say, with reference to the embodiment of FIGS. 5-8, thepump drive mechanism 268 typically comprises an electric motor and apower supply that provides the necessary current to run the motor.Constant current can be attained by directing the voltage from the powersupply to an amplifier which adjusts and controls the fluctuatingvoltage input to provide a constant current output to the motor. With aconstant current supplied to the electric motor that runs the pump, themotor provides for constant torque to the pump head in the disposableheat exchange unit/cassette, which ultimately provides for constantpressure supplied to the fluid to the catheter.

Therefore, in one embodiment of the disposable cassette of theinvention, the cassette comprises an external heat exchanger having aninlet and an outlet, a first fluid supply line in fluid communicationwith the heat exchanger inlet, a disposable pump head having a pumpinlet in fluid communication with the heat exchanger outlet and having apump outlet, a second fluid supply line in fluid communication with thepump outlet for receiving fluid pumped out of the pump outlet, and anoptional pressure regulator in fluid communication with the pump outletfor regulating the pressure of fluid pumped from the pump head. The pumphead is actuated by an electric motor that is controlled by an amplifiercontroller, where the amplifier controller supplies a constant currentto the pump head thereby causing the pump head to supply a relativelyconstant pressure to the fluid in the second fluid supply line.

Exemplary Pump

The pump section 552 is readily adapted for use with the reservoirsection 550 and feedblock section 554 of the heat exchange cassette ofFIG. 13A or the reservoir section 450 of the heat exchanger and 400 a ofFIG. 10A, and is configured to allow for pumping of heat exchange fluidat a constant pressure. In this embodiment of the invention, the pumpingmechanism creates rapid flow in a heat exchange fluid supply system forsupplying a heat exchange fluid to an intravascular heat exchangecatheter, and comprises a cavity having a quasi-cardioid shape, an inletto the cavity, an outlet from the cavity, a pump head comprising a rotorhaving a central groove, and a vane slidably mounted in the groove andimpinging on the edge of the cavity.

An exemplary vane-type pump section 552 is illustrated in FIGS. 15A-15C,where the pump section 550 contains a cavity 720 of quasi-cardioid shapeand the pump head 642. The pump head 642 has a rotor 722 which iscircular and rotates within the cavity 720, and has a central groove 724disposed diametrically thereacross. A vane 726 is slidably mounted inthe groove and impinges on the edge of the cavity 720. As the rotor 722rotates around its center, the vane 726 moves freely, sliding back andforth within the groove 724, with the ends 728 a, 728 b of the vanebeing continuously in contact with the wall of the cavity 720.

With reference to FIGS. 15A and 15C, the rotor 722 is mounted to rotatewith a shaft 730 by means of a pin 732. The shaft 730 rotates within aseal 734 and a bearing 736 separated by an optional spacer 738, providedin a manner known to those of skill in the art of rotating shaftsmounted in a fluid-tight arrangement.

With reference to FIG. 15B, a fluid inlet channel 742 leads from thefeedblock section 554 and opens into the cavity 720 just beyond the edgeof the rotor 722. A fluid outlet channel 744 opens into the cavity 720on the opposite side of the rotor 722 and leads back to the feedblocksection 554. As the rotor 722 rotates, the vane 726 is in relativelyfluid tight, continuous contact with the cavity wall 740. Fluid entersinto the cavity 720 from the inlet channel 742 and is contained in thecavity between the cavity wall 740, the rotor wall 124 and the vane 726.As the rotor 722 rotates the vane 726 also moves. This causes the fluidpath to increase in area as it is filled with heat exchange fluid fromthe inlet channel 742, and then decrease in area as the vane pushes theheat exchange fluid through outlet channel 744. The outer wall 746 ofthe rotor 722 is in relatively fluid tight contact with the wall 740 ofthe cavity along arc 748 and therefore fluid cannot travel directly fromthe inlet channel 742 to the outlet channel 744 of the pump. As therotor rotates, fluid is pumped from the inlet channel 742 around thequasi-cardioid shaped cavity and pushed by the vane out the outletchannel 744. The configuration of the fluid path can be likened to a“crescent” shape, as can be seen in FIG. 15B.

The pump is designed to rotate within the range of 200-1000 rpm and tofunction for up to 72 hours. More specifically, the pump is designed tooperate for significant periods of time, for example in excess of 72hours, at fairly high rotational speeds, for example approximately 800rpm, and to operate on pump fluids at temperatures that vary betweenapproximately 0° C. and 45° C. The choice of materials should beselected to accommodate these needs. For example, the rotor 722 of thepump head is made of a rigid and durable material with adequatelubricity to sustain a long period of close contact with the cavity wall740 (FIG. 15B) while rotating without undue wear. The rotor 722 may bemade of, for example, polyvinylidene fluoride, and the vane 726 may bemade of a material such as high density polyethylene.

It is desirable that the heat exchange catheter is supplied with fluidat a relatively constant pressure at the inlet to the catheter, forexample about 40-46 psi, but wear and temperature variations may affectthe output pressure of the pump. In the embodiment which includes thepressure regulator, the pump is designed to have an output pressureslightly higher than the optimal pressure for the heat exchangecatheter, for example 42-48 psi, and the pressure is regulated down tothe desirable pressure of 40-46 psi. If the output pressure of the pumpvaries, a pressure regulator can be incorporated into the disposableheat exchange cassette to ensure that the heat exchange catheter isprovided heat transfer fluid at a relatively constant pressure. Thepressure regulator can be, for example, a pressure regulator valve asdescribed with reference to FIG. 14B, a pressure damper as seen in FIG.10D, or a constant current regulation of the pump motor.

The curved ends 728 a, 728 b on the vane 726 provide the additionaladvantage that the point of contact between the vane edges and thecavity wall 740 changes constantly through the rotation of the rotor 722and thus avoids a single wear point on the ends of the vane. This allowsthe vane 726 to rub against the wall 740 of the cavity for as long as 72hours and yet retain a relatively fluid tight contact therebetween. In apreferred embodiment, the vane is designed to fit in the cavity 720 atroom temperature with a slight clearance, for example 0.127 mm (0.005inches). This clearance is one means of accommodating the transient andsteady state thermal changes that occur during operation and allows forexpansion of the vane due to an increase in temperature duringoperation. In this manner, at the temperatures that are encounteredduring normal operation, the vane ends 728 a, 728 b will maintainadequate contact with the wall 740 of the cavity 720 for pumping.

There are numerous other vane designs that also accommodate thermalchanges so that the vane remains in continuous contact with the wall ofthe cavity and is able to move smoothly within the cavity. FIGS. 16A-16Care side views of examples of such designs. In FIG. 16A, a vane 750 isconfigured with cut-out sections 752 a, 752 b, which allow for expansionor contraction of the vane during operation. In FIG. 16B, a vane 754defines a center section 756 made of a compressible material toaccommodate expansion or contraction of the end portions 758 a, 758 bduring operation. In FIG. 16C, a vane 760 includes a center spring 762to bias the end portions 764 a, 764 b outward during operation tocontact the wall of the cavity regardless of the temperature of thevane.

One significant aspect of the invention relates to the geometry of thequasi-cardioid shaped cavity 720, as seen in FIG. 15D. Recalling FIG.15B, the cavity wall 740 includes an inlet 742 and an outlet 744thereto, and is part of the pumping mechanism of the disposable heatexchange cassette 400 b. The pump head 642 of the pumping mechanismcomprises the rotor 722 having a diameter “D” and the aforementioneddiametral groove 724 (FIG. 15A), and the vane 726 having a length “L”and slidably mounted in the groove so as to impinge on the edge of thecavity 740.

As shown in FIG. 15D, the circumference of the cavity 740 can be dividedinto four arcs 770 a, 770 b, 770 c, 770 d, where the radius “R” of eacharc has its center at the center of the rotor 722 and is measured to thecavity wall 740. For orientation purpose, the arcs 770 a, 770 b, 770 c,770 d are defined with reference to the center of the rotor 722, with abase line of 0° identified with the point midway between the inlet andthe outlet of the cavity, i.e., the line projected from the center ofthe rotor 722 and the point on the cavity wall that is midway betweenthe inlet channel 742 and the outlet channel 744 (see FIG. 15B). 0-360°angles are measured, in a clockwise fashion from the base line.

Accordingly, the four arcs are defined as follows: (a) a first arc 770 afrom 330° to 30° and having a radius R₁, (b) a second arc 770 b from150° to 210° and having a radius R₂, (b) a third arc 770 c from 30° to150° and having a radius R₃, and (d) a fourth arc 770 d from 210° to330° and having a radius R₄. The four radii are defined as follows:

R₁=D/2

R₂=L−(D/2)

R₃=(D/2)+{[(L−D)/2]·[cos(1.50+135)]}

R₄=(D/2)+{[(L−D)/2]·[cos(1.50−315)]}

Therefore, arc 770 a is circular and thus has a constant radius R₁; arc770 b is not circular since its radius R₃ changes as the angle ofrotation increases from 30° to 150°; arc 770 c is also circular and thusalso has a constant radius R₂; and arc 770 d is not circular since itsradius R₄ changes as the angle of rotation decreases from 210° to 330°.These calculations are somewhat approximate because the vane has athickness, the end of the vane also has a radius (i.e. is curved), andthe exact contact point between the vane and the wall of the cavityvaries slightly with the rotation of the rotor. Since both ends of thevane have the same radius of curvature, this imprecision is equal oneach side, and the exact shape of the cardioid cavity can be adjusted tocompensate and still maintain contact at all points between the vane andthe cavity wall.

With reference now to FIG. 15C, the shaft 730 protrudes below the rotor722 and is fitted with three wheels 772, 774, and 776 which cooperatewith the pump drive mechanism housed in the reusable master control unit404 (FIG. 9), which imparts rotational motion to the shaft and thence tothe rotor. The top most wheel 772 is a smooth alignment wheel, themiddle wheel 774 is a toothed driven wheel, and the bottom most wheel776 is another smooth alignment wheel. The driven wheel 774 can beconstructed, for example, of a plastic material such as nylon orpolyurethane. The alignment wheels 772 and 776 can be constructed, forexample, of a polycarbonate material. These three wheels cooperate witha plurality of wheels on the reusable master control unit 404, two ofwhich are depicted in FIG. 9 as guide wheels 410. A toothed drive wheel408 is driven by the pump drive mechanism 406, and is shown in FIGS. 17Aand 17B, which depict placement of the pump wheels 772, 774, and 776within the control unit 404. FIG. 17A also shows placement of a gearshield 778, which covers the receiving opening 402 in the control unit404 (FIG. 9) once the heat exchange cassette 400 b is positioned inplace.

When the heat exchange cassette 400 b is inserted into the reusablemaster control unit 404, the toothed driven wheel 774 engages thetoothed portion 780 of motor wheel 708. The driven wheel 774 and motorwheel 408 are held engaged by contact between guide wheels 410 andalignment wheels 772, 776. As can be seen in FIG. 17B, the guide wheels410 have a larger diameter top and bottom sections 782 a, 782 b,respectively, with a small diameter middle section 784. This allows thetop sections 782 a to fit snugly against alignment wheel 772 and thebottom sections 782 b to fit snugly against alignment wheel 776, whileat the same time the middle section 784 will not come in to contact withthe toothed drive wheel 774. The guide wheels can be machined as asingle spool-shaped unit or the top, middle and bottom sections can beseparate pieces that are permanently affixed together. The toothed motorwheel can also be designed to have a slightly larger top section 786 athat fits snugly against alignment wheel 772 and/or a slightly largerbottom section 786 b that fits snugly against alignment wheel 776.Preferably the motor wheel makes contact with at least one of the smoothalignment wheels.

The positioning of the alignment and guide wheels causes the teeth ofmotor wheel 408 and driven wheel 774 to mesh at the appropriate distanceso that the teeth are not forced tightly together. The diameter of thesmooth alignment wheels 772, 776 will be approximately the pitchdiameter of the driven wheel 774 to provide proper positioning of thedrive teeth. Similarly, the diameter of the top and bottom sections, 786a, 786 b, of the motor wheel 408 will be approximately the pitchdiameter of the toothed portion 780 of the motor wheel 408. This isadvantageous in imparting smooth rotational motion without impartingside forces to the drive shaft, or causing friction between the teeth byvirtue of their being jammed together. The diametral pitch of the drivenwheel 774 and the motor wheel 408 are the same; however they willtypically have different diameters. For example, a suitable diametralpitch is 48 (48 teeth per inch in diameter), which has been found toprovide adequate strength with minimal noise during operation. A typicaldriven wheel 774 will have a pitch diameter of 2.54 cm (1 inch), whilethe corresponding motor wheel 780 will have a pitch diameter of about9.53 mm (0.375 inches).

Methods for Priming the Heat Exchange Catheter System

Referring to FIGS. 18A-18C, several methods of supplying heat exchangefluid to an intravascular heat exchange catheter are illustrated byfluid flow pathways, each pathway illustrating a different embodiment ofthe heat exchange cassette of the invention. In these embodiments, fluidflows from the pump to the heat exchange catheter, returns from thecatheter and passes through the external heat exchanger, and then entersa fluid reservoir. From the reservoir, the fluid moves to the pump, andthe cycle repeats for the desired duration. An optional pressureregulator can be positioned in the fluid path moving from the pump tothe catheter. Fluid is provided from an external fluid source, which inthe embodiment of FIG. 18A enters the priming valve, and in theembodiments of the FIGS. 18B and 18C directly enters the pump head (ofcourse, as indicated in FIG. 10B, the external source of fluid may beconnected to the reservoir).

Examples of these methods and the respective fluid pathways are furtherunderstood by reference to FIGS. 10A and 13A. In general, the methodcomprises the steps of:

(a) providing power to operate a pump head;

(b) transferring fluid from an external fluid source to a chamber;

(c) pumping fluid from the chamber into a pump cavity;

(d) pumping fluid from the pump cavity to the catheter;

(e) pumping fluid from the catheter to a external heat exchanger whichis positioned in heat transfer relationship with a heater/cooler;

(f) pumping fluid from the external heat exchanger to a heat exchangefluid reservoir;

(g) pumping fluid from the heat exchange fluid reservoir into the pumpcavity; and

(h) repeating steps (d) through (g) for the duration of operation of thecatheter.

The heat exchange cassette of the invention is initially primed, thatis, filled with heat exchange fluid from an external source and excessair removed. This priming of the system of the invention can beaccomplished in numerous ways. One embodiment of the invention utilizesa “valved-priming” mechanism, and is illustrated by the embodiment ofFIGS. 13A-14E. This valved-priming mechanism involves a priming sequencehaving a valve or the like controlling temporary fluid input from anexternal fluid source, and once the system is primed, the valve preventsfurther fluid input from the external source and fluid thereaftercirculates within a closed circuit including the heat exchange cassette400 b and the attached in-dwelling catheter. In the embodiment of FIGS.13A-14E, the valved-priming mechanism 670 is contained within a discreteunit, namely the feedblock section 554. It is understood however, thatthe valved-priming mechanism can be located in another portion of thebulkhead 430 b, for example as part of the pump section 552 or reservoirsection 550, and still serve the same function.

The invention also encompasses a method for automatically commencing andceasing the priming of a heat exchange fluid supply system for supplyinga heat exchange fluid from an external fluid source to an intravascularheat exchange catheter, using the means described above. This methodcomprises the steps of:

(a) providing power to operate the pump, wherein the reservoir is notfilled to capacity and the valve is in its first position and the pumpoperates to pump fluid:

a. from the external fluid source through the fluid providing line intothe fill port of the chamber and out of the fluid outlet into the pumpcavity;

b. from the pump cavity to the fluid return line to the catheter;

c. from the catheter through the fluid supply line to the external heatexchanger inlet orifice;

d. from the external heat exchanger outlet orifice to the heat exchangefluid reservoir; and

e. into the heat exchange fluid reservoir to fill the reservoir;

(b) filling the reservoir to capacity; at which point

(c) the optical fluid level detector operates to move the valve to itssecond position and the pump operates to pump fluid from the heatexchange fluid reservoir to the fluid inlet of the chamber and out ofthe fluid outlet into the pump cavity.

When the disposable heat exchange cassette 400 b of the invention isfirst put into operation, the unit is initially filled with heatexchange fluid from an external fluid source such as an IV bag of salineattached to the fill port 632 leading to the fill channel 634. Inaddition, the linear actuator 418 of the valve actuation system 416 isactivated, to place the priming valve 670 in its first position (FIG.14E) with the valve member 676 depressed sufficiently to allow fluid toflow from the IV bag into the valve chamber 636. More specifically,during a priming operation, the push rod 420 in the receiving opening402 of the control unit 404 seen in FIG. 9, passes through the primingvalve aperture 618 in the cover plate 442 b (FIG. 13A) and displaces theflexible membrane 672 downward which, in turn, displaces the valvemember 676 downward, as seen in FIG. 14E. The lower O-ring 692 on thevalve member 676 thus contacts and seals against the floor of the middlesubchamber 682 b, permitting fluid to flow from the fill channel 634into the upper subchamber 682 a, through the middle subchamber 682 b,and through the outlet channel 642 toward the pump head 552. In thismanner, heat exchange fluid from external fluid source 630 (FIG. 13B)enters the feedblock section 554, and then flows into the pump section552. From the pump section 552, the fluid is pumped out through pressureregulating chamber 646, the outlet channel 648 and outlet port 650, andto the catheter inflow line 652 leading to the heat exchange catheter.Fluid is thereafter circulated through the catheter, back through thecatheter inflow line 654 that couples to an inlet port 656 of thefeedblock section 554, through the flow through channel 660 within thepump section 552 leading to a bulkhead outlet 662. Fluid enters andpasses through the external heat exchanger 440 b and back into thereservoir section 550. As the fluid is pumped into the reservoir section550, air displaced by the fluid escapes through the hydrophobic vents588. This generally continues until the system is full of heat exchangefluid and excess air has been vented out of the system. At this point inthe process, the valve 670 is closed from the external fluid source 630(by, e.g., automatic release of the push rod 420) and the fluid supplycircuit between the catheter and the heat exchange cassette 400 b isclosed.

The reservoir section is provided with a means to detect when the fluidreservoir is full, as described below, whereby signals are provided tothe reusable master control unit that represent the level of the heatexchange fluid in the reservoir. Using these data, the reusable mastercontrol unit adjusts the linear actuator 416 so that the position of thevalve 670 changes and the fluid flow path is altered. Thus when thefluid level in the reservoir section 550 rises to a sufficient level, asignal is sent to the reusable master control unit to deactivate thelinear actuator 416 so that it moves to a released position, thuswithdrawing the push rod 420, resulting in the valve member 676 beingbiased back to its second position (FIG. 14D). In this second position,fluid from the now full reservoir is directed through the feedblocksection 554 to the pump section 552, while fluid flow from the externalfluid source is diminished or ceases entirely.

In a preferred embodiment the pump would continue to run for a period oftime after the level sensor indicated that the system was full to ensurethat any air bubbles in the catheter or the external heat exchanger orthe bulkhead would be expelled into the reservoir section 550 where theycould vent to the atmosphere. Since the fluid is being drawn from thebottom of the reservoir through reservoir outlet channel 561 (FIG. 13E),and air moves up towards the top of the reservoir where the hydrophobicvents 588 are located, this acts to purge air from the system.Therefore, it is important to realize that the priming valve 670 mayalso have a third position that is an intermediate position from itsfirst and second positions described above. In this manner, heatexchange fluid may enter the central chamber 636 from either thereservoir or the external fluid source, or both simultaneously if thepriming valve 670 is opened to this intermediate position. So, forexample, in an embodiment of the intention that utilizes the pump in afirst, intermediate and then second position, fluid would enter the pumpsolely from the external fluid source (first position, FIG. 14E), thenfluid would enter the pump in part from the external fluid source and inpart from the reservoir section 550 (intermediate position) and finallyfluid would enter the pump solely from the reservoir section 550 (secondposition, FIG. 14D).

It should be noted that priming of the system occurs prior to theinsertion of the heat exchange catheter into the patient, with the heatexchange balloon outside the body. Indeed, the heat exchange balloon isdesirably restrained within a tubular sheath, or is otherwise radiallyconstrained, to prevent inflation thereof during priming. Once primingis complete, the catheter and sheath are inserted to the desiredlocation within the patient, typically the vasculature, and the sheathcan then be removed. The sheath thus assists in maintaining a radiallycompact profile of the catheter during intravascular insertion, whichprevents injury and facilitates the insertion so as to speed up theprocedure.

Referring to the embodiment of FIGS. 13-15 and the flow diagram of FIG.18A, a method for supplying heat exchange fluid to an intravascular heatexchange catheter comprises the steps of:

(a) transferring fluid from an external fluid source 630 to a fluidreservoir 550;

(b) providing power to operate a pump head 642;

(c) venting air from the fluid reservoir section 550 as the air isdisplaced by the fluid from the external fluid source;

(d) pumping fluid from the fluid reservoir section 550 through a pumpcavity 720, to a heat exchange catheter, via an external heat exchanger440 b which is positioned in heat transfer relationship with aheater/cooler, and pumping the fluid and air displaced by thecirculating fluid from the external heat exchanger 440 b to the fluidreservoir 550;

(e) venting the air displaced by the circulating heat exchange fluidfrom the fluid reservoir section 550;

(f) repeating steps (a) through (e) for the duration of operation of thecatheter.

Preferably a step for measuring the fluid level in the heat exchangefluid reservoir is included to insure that the reservoir remains full.Such a step can also comprise using an optical fluid level detector todetermine the fluid level, where step (h) begins when the reservoir isfilled to capacity and step (b) ceases when step (h) begins. The methodfor supplying heat exchange fluid to a catheter for the embodiment ofFIG. 10A uses a passive-priming mechanism, while the method for theembodiment of FIG. 13A uses a unique valved-priming mechanism, describedin detail above. In the priming mechanism shown in FIG. 10A, the fluidlevel measuring step may also comprise using an optical fluid leveldetector to determine the fluid level, where step (g) begins when thereservoir is filled to capacity and step (b) ceases when step (g)begins.

More particularly, the embodiment of FIGS. 10A-10D provides themechanism for passively priming the system with heat exchange fluid froman external source 454. The external fluid source 454 is generally hungor placed at a location above the reservoir 450, and is connected by afluid providing line 456 to the reservoir. The reservoir 450 has a fillport 476 connected to the fluid providing line 456, and thus fluid flowsinto the reservoir 450 which communicates with the pump section 452,thus priming the pump head 490. Initially, with the catheter out of thepatient's body and sheathed, the pump is operated to draw heat transferfluid from the external fluid supply and circulate it through thesystem. The air that is in the system is vented through the hydrophobicair vents. When the pressure in the system is equal to the head pressurefrom the external fluid source (this will happen at a level whichdepends on the pump pressure and the height of the external fluid sourceabove the reservoir) the system will essentially be in equilibrium andwill cease drawing fluid from the external source. At this point thecatheter and heat exchange cassette system will be considered to beprimed. The heat exchange catheter will generally thereafter be insertedinto the patient, and as the system is operated, any fluid required tobe added to the system to maintain the pressure equilibrium mentionedabove will be drawn from the external source which is in fluidcommunication with the reservoir through the fluid providing line.Likewise, any buildup of pressure in the system due, for example to theheating and expanding of the system, will be relieved by fluid flowingback into the external fluid supply source 454. Because of the abilityof the system to react to minor expansions and contractions of fluidsupply, there is no need to monitor the high level of fluid, and onlyredundant sensors of the low level need be incorporated into the heatexchange cassette. This has the advantage of automatic maintaining arelatively uniform fluid level without the need for sensors and thelike.

Safety Systems

The reservoir section can be provided with a means to monitor the amountof heat exchange fluid that is in the system, more specifically anoptical means for detecting the level of fluid contained within thefluid reservoir. Since the heat exchange fluid is a biocompatible fluidand the volume of the external source is only about 250 ml, it is notexpected that fluid leakage into the patient will be problematic. Itwould be very undesirable, however, to have the fluid level fall so lowthat air is pumped into a patient. Therefore the heat exchange fluidsupply system of the invention is designed to detect the level of thefluid in the system so that a warning or other measure can be institutedif the system becomes unacceptably low. In a preferred embodiment, twoprisms in the bulkhead reservoirs, each having a corresponding beamsource and sensor, are utilized. Each prism will have a correspondingbeam source and sensor mounted on the reusable master control unit at alocation adjacent to the prism. For example, FIG. 9 illustratesplacement of an optical beam source 412 and optical beam sensor 414 forthe first prism 590 a in the bulkhead design of FIGS. 13A-13E. As seenin FIG. 13E, the transparent window 591 configured in the end of thereservoir container 580 allows for optical observation of the fluidlevel in the reservoir cavity 584. An adjacent beam source and sensorwould also be provided for the second prism 590 b, if present.

For the bulkhead design of FIG. 10A, the beam source(s) and sensor(s)would be positioned on the control unit 404 at a location underneath thefirst and second prisms 486 a, 486 b. For example, the fluid levelmeasurement sensor module 276 mounted on the underside of the lowerguide assembly 266 in FIG. 6B may include optical transmitters/sensorsthat are placed in registry with the transparent window 316 so as tointeract with the heat exchange cassette and provide an indication offluid level within the unit. The prisms have a diffraction surface andmay be machined separately using a material such as polycarbonate andthen affixed within the reservoir section, or they may be machined aspart of the section. Again, although only one prism is needed for thefluid level detection method to function, it may be desirable to includea second redundant prisms described below.

The second prism/source/sensor is redundant and functions to monitor thesame fluid level as the first prism but operates as a safety mechanismin the even the first prism/source/sensor fails to function properly.Alternatively, one of the prisms may also have a “high level” sensingsystem that can be used to signal the control unit when the fluid in thereservoir reaches a certain high level. This is useful, for example,when the valved-priming system is used and detection of a high or fulllevel is needed to determine when to activate the valve to stop thepriming sequence. If desired, both high level and low level sensors canbe employed on each prism. The sensors will generate a signal indicatingthat either there is or is not fluid at the level of the optical beam.If the optical beam source and sensor are positioned or the optical beamis directed near the top of the tank, the indication that the fluid hasreached that level will trigger the appropriate response from thecontrol system, for example to terminate a fill sequence. On the otherhand, if the sensor is positioned or optical beam directed to sense thefluid level on the bottom of the tank, then the fluid level detector isconfigured to detect a low fluid level and can generate a signalrepresenting such low level. The heat exchange cassette can then beconfigured to respond to this signal indicative of a low level of fluidin the reservoir. For example, the pump head can be designed to beresponsive to this signal such that the pump head stops pumping when alow fluid level is detected, so that air will not be pumped into theheat exchange catheter. In addition, an alarm may sound and an alarmdisplay, such as the display 200 of FIG. 5C, may be activated to alertthe operator to the low fluid level condition.

In a preferred embodiment of the invention, the reservoir section isprovided with a means to detect when the fluid reservoir is too low. Inoperation, the optical beam source is turned on to produce an opticalbeam that is directed towards the bottom of the prism and is reflectedback to the optical beam sensor. Typically, this source would beginoperation after the reservoir had started to fill with fluid. Thus,fluid would be in the reservoir and so the sensor will not observe areflected light beam. As long as this is the case, the pump willcontinue to operate, moving fluid through the heat exchange cassette andcatheter. However, if the fluid level drops below the level of theoptical beam, the sensor then will observe a reflected light beam, whichwill trigger the pump to cease operation and the system to shut down.

In the embodiment of the invention that involves a valved-primingsequence, the optical beam source is turned on to produce an opticalbeam that is directed towards the top of the prism and is reflected backto the optical beam sensor. As long as the sensor observes a reflectedlight beam, the fill or priming operation of the heat exchange cassettecontinues to run. As the fluid level rises, at some point it reaches alevel such that the optical beam is deflected and no longer reflectsback to the sensor. When the sensor no longer observes a reflected lightbeam, the priming operation of the heat exchange cassette ceases.Thereafter, the fluid level detector is configured to detect a low fluidlevel and a high fluid level, and the detector generates a first signalrepresenting the low level and a second signal representing the highlevel. Initially, the valve is in its first position and is maintainedin this first position in response to the first signal thereby allowingfluid to enter reservoir until it reaches a high level, at which pointthe detector generates a second signal, and the valve is actuated to itssecond position. With specific reference to FIGS. 14A and 14D-14E, thevalve member 676 of the priming valve 670 is biased into the “second”position (FIG. 14D), enabling fluid flow between the reservoir section550 and pump section 552 via the feedblock section 554. The circulationsystem of the catheter and heat exchange cassette is thus closed. In the“first” position of the valve member 676 (FIG. 14E), fluid from theexternal source is permitted to flow into and supplement the otherwiseclosed fluid circulation system.

Additional safety systems that are contemplated by the invention includebubble detectors at various locations on the flow lines to detect anybubble that may be pumped into the fluid system and temperature monitorsthat may signal if a portion of the system, or the fluid, is at atemperature that is unacceptably high or low. A detector to indicatewhether the fluid sensor optical beam sources are operational may besupplied, for example by placing a detector located to detect theoptical beam initially when the system is turned on but there isinsufficient fluid in the reservoir to cause the beam to diffract backto the detector. The control unit depicted in FIGS. 1,2 and 5 providefor multiple patient temperature sensors. A warning may sound, and thesystem may shut down, if the temperature signal from the two differentsensors are dramatically different, indicating that one of the sensors,perhaps the one driving the control of the system, is misplaced, is notfunctioning, has fallen out or the like. Other similar safety andwarning systems are contemplated within the scope of the system of theinvention.

While particular embodiments of the invention have been described above,for purposes of or illustration, it will be evident to those skilled inthe art that numerous variations of the above-described embodiments maybe made without departing from the invention as defined in the appendedclaims.

We claim:
 1. A heat transfer catheter system, comprising: a heattransfer catheter insertable into a patient; a disposable heat exchangeplate having two layers, a stiff back plate and a thinner heat exchangelayer bonded thereto, the pattern of bonding between the two layersdefining a serpentine pathway; conduits coupled to the heat transfercatheter and heat exchange plate that enable circulation of a heatexchange medium therebetween; and a master control unit housing aheater/cooler unit within and having a slot, the slot being sized sothat the disposable heat exchange plate can be installed therethroughinto the master control unit and into thermal communication with theheater/cooler unit, wherein the heater/cooler unit can influence thetemperature of the patient via the disposable heat exchange plate,conduits, and heat transfer catheter.
 2. The system of claim 1, whereinthe slot in master control unit defines a cavity into which the heatexchange plate installs, wherein fluid flow through the serpentinepathway causes inflation of the thinner heat exchange layer relative tothe stiff back plate and subsequent compressive retention of the heatexchange plate within the cavity.
 3. The system of claim 1, wherein thedisposable heat exchange plate incorporates an integral pump headadapted to move the heat exchange medium through the serpentine pathway.4. The system of claim 3, wherein the master control unit houses a pumpdriver adapted to engage and power the integral pump head when thedisposable heat exchange plate is installed in the slot.
 5. The systemof claim 3, wherein the disposable heat exchange plate furtherincorporates a reservoir for storing a quantity of the heat exchangemedium.
 6. The system of claim 1, wherein the heater/cooler unitcomprises a thermoelectric heater/cooler.
 7. The system of claim 1wherein the master control unit includes a microprocessor configured toreceive a target temperature input and a sensor signal that represents asensed patient temperature, the microprocessor being configured to addheat to the heat exchange medium if the target temperature is above thepatient temperature and remove heat from the heat exchange medium if thetarget temperature is below the patient temperature, and wherein themicroprocessor responds to the signal from the sensor with aproportional integrated differential (PID) response such that the rateat which patient temperature approaches the target temperature iscontrolled.
 8. A heat transfer catheter system, comprising: a heattransfer catheter insertable into a patient; a disposable heat exchangeunit having a stiff back plate and a thinner heat exchange layer bondedthereto, the pattern of bonding between the stiff back plate and thethinner heat exchange layer defining a serpentine fluid pathwaytherewithin and incorporating an integral pump head adapted to movefluid through the fluid pathway; conduits coupled to the heat transfercatheter and heat exchange unit that enable circulation of a heatexchange medium therebetween upon operation of the pump head; and areusable master control unit having a heater/cooler and a pump driver,the disposable heat exchange unit being adapted to couple to the mastercontrol unit such that the pump driver engages the integral pump headand so that the fluid pathway is in thermal communication with theheater/cooler.
 9. The system of claim 8, wherein the master control unitdefines a cavity into which the heat exchange unit couples, whereinfluid flow through the serpentine pathway causes inflation of thethinner heat exchange layer relative to the stiff back plate andsubsequent compressive retention of the heat exchange unit within thecavity.
 10. The system of claim 8, wherein heater/cooler comprises athermoelectric heater/cooler.
 11. The system of claim 8, furtherincluding a plurality of sensors supplying patient data to the mastercontrol unit, the master control unit being adapted to operate theheater/cooler based on the supplied patient data.
 12. The controller ofclaim 11, wherein the master control unit comprises a microprocessorresponsive to each of the sensors to control the heater/cooler, whereinthe microprocessor is configured to compare the signals from at leasttwo of the plurality of sensors and produce an alarm condition when thesignals do not agree.
 13. The controller of claim 8, wherein themicroprocessor further receives a target temperature input and a sensorsignal that represents a sensed patient temperature, the microprocessorbeing configured to add heat to the heat exchange medium if the targettemperature is above the patient temperature and remove heat from theheat exchange medium if the target temperature is below the patienttemperature, and wherein the microprocessor responds to the signal fromthe sensor with a proportional integrated differential (PID) responsesuch that the rate at which patient temperature approaches the targettemperature is controlled.
 14. The system of claim 8, further includinga slot provided in the master control unit, the disposable heat exchangeunit being plate-shaped so as to fit within the slot and couple with themaster control unit.
 15. The system of claim 8, wherein the disposableheat exchange unit further incorporates a reservoir for storing aquantity of the heat exchange medium.
 16. The system of claim 15,further including at least one optical sensor for sensing the level ofheat exchange medium within the reservoir.
 17. A method of regulatingthe temperature of at least a portion of a patient, comprising:providing a disposable heat transfer catheter having a heat transferregion and a heat exchange unit having a pump head, the heat transfercatheter and heat exchange unit coupled via conduits that enablecirculation of a heat exchange medium therebetween; providing a mastercontrol unit housing a heater/cool unit within and having a slot;installing the heat exchange unit through the slot into the mastercontrol unit and into thermal communication with the heater/cooler unit;inserting the heat transfer catheter into the patient; sensing thepatient's body temperature; selecting a target temperature differentthan the body temperature; circulating fluid between the heat transfercatheter and heat exchange unit in the master control unit, the heatexchange unit, heater/cooler unit, and pump head being adapted to flowheat exchange medium through the conduits to elevate or depress thetemperature of the catheter heat transfer region relative to the bodytemperature; and transferring heat between the heat exchange unit and aheater/cooler unit so as to regulate the temperature of the patient viathe heat transfer catheter; selecting a ramp rate equal to the time rateof change of temperature from the body temperature to the targettemperature; setting the temperature of the heat exchange medium withinthe catheter heat transfer region based on the ramp rate; monitoring thetemperature differential between the target temperature and the bodytemperature; and reducing the ramp rate when the temperaturedifferential reduces below a predetermined threshold.
 18. The method ofclaim 17, wherein the disposable heat exchange unit includes aserpentine pathway through which the heat exchange medium flows, andcirculating includes circulating the heat exchange medium back and forththrough the serpentine pathway.
 19. The method of claim 17, wherein thedisposable heat exchange unit incorporates a fluid pathway and anintegral pump head, and circulating includes driving the pump head. 20.The method of claim 19, wherein the master control unit houses a pumpdriver, and installing comprises engaging the pump driver with the pumphead.
 21. The method of claim 17, wherein heater/cooler unit comprises athermoelectric heater/cooler, and transferring comprises either heatingor cooling the temperature of the patient based on the polarity that thethermoelectric heater/cooler is operated.
 22. The method of claim 17,further including a plurality of sensors supplying patient data to themaster control unit, the method further including operating theheater/cooler unit based on the supplied patient data.
 23. A heattransfer catheter system, comprising: a heat transfer catheterinsertable into a patient; a disposable heat exchange plate; conduitscoupled to the heat transfer catheter and heat exchange plate thatenable circulation of a heat exchange medium therebetween; a pluralityof sensors for monitoring at least one selected parameter of a patientand for providing signals representative of the at least one selectedparameter; supplying patient data to the master control unit, the mastercontrol unit being adapted to operate the heater/cooler unit based onthe supplied patient data; a master control unit housing a heater/coolerunit within and having a slot, the slot being sized so that thedisposable heat exchange plate can be installed therethrough into themaster control unit and into thermal communication with theheater/cooler unit, the master control unit including a microprocessorresponsive to each of the plurality of sensors to control theheater/cooler unit, the microprocessor being configured to compare thesignals from at least two of the plurality of sensors and produce analarm condition when the signals do not agree, and wherein theheater/cooler unit can influence the temperature of the patient via thedisposable heat exchange plate, conduits, and heat transfer catheter.24. The system of claim 23, wherein the disposable heat exchange plateincludes a serpentine pathway through which the heat exchange mediumflows.
 25. The system of claim 1, wherein the heat exchange platecomprises two layers, at stiff back plate and a thinner heat exchangelayer bonded thereto, the pattern of bonding between the two layersdefining a serpentine pathway.
 26. The system of claim 25, wherein theslot in master control unit defines a cavity into which the heatexchange plate installs, wherein fluid flow through the serpentinepathway causes inflation of the thinner heat exchange layer relative tothe stiff back plate and subsequent compressive retention of the heatexchange plate within the cavity.
 27. The system of claim 23, whereinthe disposable heat exchange plate incorporates a fluid pathway and anintegral pump head adapted to move the heat exchange medium through thefluid pathway.
 28. The system of claim 27, wherein the master controlunit houses a pump driver adapted to engage and power the integral pumphead when the disposable heat exchange plate is installed in the slot.29. The system of claim 27, wherein the disposable heat exchange platefurther incorporates a reservoir for storing a quantity of the heatexchange medium.
 30. The system of claim 23, wherein the heater/coolerunit comprises a thermoelectric heater/cooler.
 31. The controller ofclaim 23, wherein the microprocessor further receives a targettemperature input and a sensor signal that represents a sensed patienttemperature, the microprocessor being configured to add heat to the heatexchange medium if the target temperature is above the patienttemperature and remove heat from the heat exchange medium if the targettemperature is below the patient temperature, and wherein themicroprocessor responds to the signal from the sensor with aproportional integrated differential (PID) response such that the rateat which patient temperature approaches the target temperature iscontrolled.
 32. A heat transfer catheter system, comprising: a heattransfer catheter insertable into a patient; a disposable heat exchangeunit having a fluid pathway therewithin and incorporating an integralpump head adapted to move fluid through the fluid pathway; conduitscoupled to the heat transfer catheter and heat exchange unit that enablecirculation of a heat exchange medium therebetween upon operation of thepump head; a plurality of sensors for measuring at least one patientparameter and for generating signals representative of a value of the atleast one patient parameter; and a reusable master control unit having aheater/cooler and a pump driver, the disposable heat exchange unit beingadapted to couple to the master control unit such that the pump driverengages the integral pump head and so that the fluid pathway is inthermal communication with the heater/cooler, the master control unitalso having a microprocessor responsive to each of the plurality ofsensors to control the heater/cooler, the microprocessor also configuredto compare the signals from at least two of the plurality of sensors andproduce an alarm condition when the signals to not agree.
 33. The systemof claim 32, wherein the fluid pathway in the disposable heat exchangeunit is serpentine.
 34. The system of claim 33, wherein the heatexchange unit comprises two layers, a stiff back plate and a thinnerheat exchange layer bonded thereto, the pattern of bonding between thetwo layers defining the serpentine pathway.
 35. The system of claim 34,wherein the master control unit defines a cavity into which the heatexchange unit couples, wherein fluid flow through the serpentine pathwaycauses inflation of the thinner heat exchange layer relative to thestiff back plate and subsequent compressive retention of the heatexchange unit within the cavity.
 36. The system of claim 32, whereinheater/cooler comprises a thermoelectric heater/cooler.
 37. Thecontroller of claim 32, wherein the microprocessor further receives atarget temperature input and a sensor signal that represents a sensedpatient temperature, the microprocessor being configured to add heat tothe heat exchange medium if the target temperature is above the patienttemperature and remove heat from the heat exchange medium if the targettemperature is below the patient temperature, and wherein themicroprocessor responds to the signal from the sensor with aproportional integrated differential (PID) response such that the rateat which patient temperature approaches the target temperature iscontrolled.
 38. The system of claim 32, further including a slotprovided in the master control unit, the disposable heat exchange unitbeing plate-shaped so as to fit within the slot and couple with themaster control unit.
 39. The system of claim 32, wherein the disposableheat exchange unit further incorporates a reservoir for storing aquantity of the heat exchange medium.
 40. The system of claim 39,further including at least one optical sensor for sensing the level ofheat exchange medium within the reservoir.